The shadows pressed down like weighted yokes, filled with the dusty age of untouched caverns. Thick, damp air clouded the party’s lungs as they clung to the light of their torches. Their eyes flashed across the cave walls, mistaking shadows and rock formations for all manner of monsters. But they could not hope to see everything. The caves wanted them to be blind and afraid, and the group’s ability to fight that was waning. A rock fell, disturbed by movement. Its sound echoed through the chamber, repeating from every direction. Something was approaching, but from where?
We’ve covered a number of the most common environments but we’re not done yet. It’s time to head below the surface. Whether that means a tunnel, cave, cavern, or the Underdark itself, we continue our goal of giving you new ideas and approaches to your game’s encounters. Each and every one comes with a flavorful introduction, description on how to plan and run the cave encounter, and different ways to change it for your own table. We want to inspire you while giving some useful tips and maps to make your job as easy and enjoyable as possible.
Table of Contents
1 – The party comes to a basilisk lair, their torchlight allowing them to see into its eyes.
As they travel through the caves, the adventuring group begins to notice broken chips and shards of stone at their feet. They show signs of once being detailed and intricate but have since fallen to pieces. The stones grow larger and more defined as the adventurers progress, their nerves gradually unsettling. The shapes appear almost… natural. Organic. But it is only when they reach a larger chamber that the truth is confirmed. They look around anxiously, seeing the rocks coalesce in the shapes of native wildlife and other unfortunate explorers. As the group turns to anxiously retreat, the scraping of claws echoes behind them.
For our first cave encounter, we want to look at how the subterranean environment can add to a more standard encounter. The key dynamic here is the use of light and how that affects the group’s combat ability. See, normally darkvision is a strength with little to no drawback. Many races take it for granted and its presence can often create a challenge for encounters that might rely on darkness or visual obstruction. But here it is a weakness. The basilisk relies on its prey seeing it (and vice versa), so players with darkvision must rely on averting their gaze. Humans and other races have the option of snuffing or manipulating their light to gain possible advantages.
Players with darkvision still have the option to avert their eyes, so attacks with disadvantage will be common either way. The difference is that a player starting their turn without being able to see a basilisk won’t need to look away and therefore can use that to intelligently bypass the disadvantage. It’s a brief moment of opportunity but gives your party some extra options for strategy.
This encounter’s introduction is important for not immediately alerting your party. We start with them finding the larger chunks of stone to begin building tension without giving away what is happening. The truth is that these are the pieces left behind from the basilisk’s meals. Players can find larger or more identifiable chunks (lower DC to identify features) as they move closer to the lair but the reveal should only come in the final moments before initiative. This is where they will find the petrified victims that the monstrosity has dragged inside but not yet consumed. The party is ultimately still able to flee, though they will have to get past the basilisk cutting off their escape.
From there, combat is relatively simple. Fill the cavern with supporting columns and rocks for cover, as well as pockets of bioluminescent moss. This can create small areas of light that the basilisks use to ensure their prey can see them, giving your party an interesting dynamic to focus on rather than simply dealing damage. Let your players use these features creatively and be ready to accommodate their ideas. Finally, if you wish to lessen the steep penalty of petrification, include an antidote in the hands of a previous victim. Players can heal one victim with it, be it a party member or other character, or keep it as a reward to more easily overcome a future encounter. If more than one person is petrified, you can allow them the possibility of creating antidotes by brewing the eyes of a recently dead basilisk.
2 – The cave transitions into the mouth of a great beast, hungry for careless travelers.
The cave tunnel continues through the dark, rough and covered in stalagmites and stalactites. Though the party remains alert for danger, the tedious lack of differentiation in the environment has a way of dulling one’s senses. It has already changed before they realize it. The formations jutting from the floor and roof seem to be of a different material, the colors beneath their orange torchlight have changed, and the ground is… wet? Focusing more on their surroundings, the group’s stomachs all drop at a final realization: the walls are pulsing and shifting, ever so slightly. They have transitioned from a tunnel and into the gullet of an enormous beast at some point, and it is now beginning to digest them.
This cave encounter aims to be a quick diversion that asks the players to quickly react. The beast, likely a worm, has evolved to hunt this way and therefore is well-disguised as a continuation of the cave. It should be a slow transition, meaning that your travel description should not give anything away. Describe the tunnel as it continues, making note first of the stalagmites and stalactites. You can mention a small crack where the beast’s mouth begins and the dank, breathy air afterward, but be sure not to use a tone of danger in your voice. It is up to your players to investigate, should they suspect something. Otherwise, your reveal will come once they are deeper in. The worm will close its mouth some distance behind them and its body will begin digesting and chewing.
If your party identifies the danger before this point, it is up to them to sneak out without alerting it. Trying to walk out will still lead to it eating them, of course, though they will be much closer to the exit. When this does happen, it will have two effects. The first will be a mist of digestive enzymes that force constitution saves on each of its turns (success halving the damage). We add a save because of it being a mist and the party not being restrained, as with other creatures that can swallow prey. Meanwhile, the worm’s turns will also include chewing the players. Choose or roll for a number of five-foot lines running across the cave, different ones every turn, and have anything in those areas make a dexterity save. Successes can take half damage, while failures can render them prone as the teeth crush them.
Another way to run this encounter is by shifting gear to comedy. Instead of camouflaging the mouth, have a perceptive character notice the change when they reach it. They can quickly identify that the flesh and teeth, and will then (hopefully) not walk in. A few minutes of standing around later, have the worm move. It can begin speaking, asking for them to step inside as it has been days since anything has fallen for its trap and it’s starving. Play it as goofy and inept, attempting to bargain with or simply beg the party. Perhaps they can even find a way of making a deal with the worm?
Ultimately, both of these should lead to the worm moving on without having eaten the party. It can begin burrowing into the side of the cave, eventually disappearing entirely. The party can then continue on through the larger tunnel that it had dug to reach that point.
3 – A vertical tunnel cuts through a chamber, seeming to repeat endlessly.
The party comes to a larger, circular chamber. Their tunnel cuts through it, intersecting with another shaft that runs vertically through the center. Curiosity compels them to investigate the shadowy pit, finding that it extends further than of them can see. They toss a torch down, watching as it falls into darkness. A few moments later, a lit torch falls from the tunnel above and continues down the pit. Another few moments and the torch repeats again. Only this time, it disturbs something in the tunnels. A frenzied swarm of wings, claws, and teeth fly from both openings, bombarding the party with attacks.
The premise of this cave encounter comes from the location it uses. This makes the combat itself extremely dynamic. Our most basic idea is for swarms of bats to fly out of the shaft with a smaller number of darkmantles. The latter’s use of darkness and blinding can help elevate the danger of the pit, particularly if you include (minor) additional mechanics to simulate actual blindness. One option is to describe the darkmantle colliding with the player when it attacks, sending them spinning. Roll a d8 and use the result to determine which direction they are now facing, but do not tell the player themself. They can still use a perception or investigation check to find out, or another party member can yell at them. That is where the darkmantles’ Darkness Aura can come in. When the player moves, they risk walking into the pit.
Another option is to use the pit more directly. Replace the flying swarms with creatures that can pull or forcibly move players. The most obvious choice is ropers, though grells or a gibbering mouther are other, more magical options. These creatures might have been drawn by the pit’s magic. Their abilities mean that, while they might not be intentionally throwing prey down the hole, it is still very likely that a player will end up falling. This is where the cave encounter’s unique challenge comes into play.
Falling in will have a player descend for a turn before it repeats and they pass the chamber again. This gives them an opportunity to escape every turn, meaning they are not left out of combat if they are dragged in early. As always, let your players think creatively about a solution. Feather fall is the most obvious choice but be ready for them to come up with other insane, unrealistic ideas. You might wish to be lenient with fall damage to prevent lower-level characters from splattering against the stone rim. Just don’t immediately indicate to players that you’re doing so. It is better to have them think about the real danger and come up with a genuine solution, and then lower the damage if you need to.
4 – The tunnel ahead is flooded and something invisible is lurking in the water.
A slow descent in the party’s path brings them to the surface of a flooded cavern. It is the only way forward, requiring them to dive under and find their way to the other side. The water is dark and cold, and will snuff most nonmagical lights. Fortunately, there are several pockets of air that allow the group to stop and breathe as they move. As they do, something brushes past the leg of the rear-most adventurer. They whip around but can see nothing. The cavern opens again, not long after, allowing them a momentary reprieve. But it is as they stop that the water begins to move; not something below the surface, but the liquid itself.
This is another of our cave encounters that uses a unique battlefield as its basis. Unlike the previous portal-pit, this time we use a section of the cave network that has been flooded. Players will need to first overcome the environmental obstacle by diving through a submerged tunnel, before entering a larger chamber. This is where the combat will take place. Having to swim through is simple enough and will ultimately not require many checks. Encourage your players take some precautions as they move through, such as conjuring light or managing to seal the air in lanterns, as well as searching for air pockets. You can make the tunnel long enough that at least one of them will need to take a breath. Being underwater can halve the range of light sources and darkvision, in addition to the disadvantages in combat.
The entry tunnel will lead to a nexus chamber. This should be more open and with plenty of air and other tunnels out. The water can fill two-thirds of the room, with all other exits below that to add risk to trying to escape from the combat. Support columns and changes in elevation will form crude islands above the surface. Position these in ways that give players different options but try to avoid making too many of them too large, as the enemy creatures will need to reach them. Include bones on the cavern floor if you want to give players some extra warning on top of something brushing past them. The closer they are to the center, the more evidence of previous victims.
Speaking of creatures, our choice of monster is where this all comes together. The water is home to a water elemental and minion water weirds. The elemental will coalesce from the water and use it to obscure its movement while its smaller minions can remain entirely hidden until striking. They will use this to grab the party and pull them under the surface, pummeling and drowning them. From here, the combat is relatively simple and dependent on your party’s plan. They may stay and fight or attempt to flee and risk swimming through another tunnel.
Be very careful when balancing your creature numbers, given the effects of drowning. The risk of being knocked unconscious while underwater can elevate the threat that the creatures pose so you may wish to err on the side of caution. I have personally had a game in which the party’s monk was dragged under and pummeled. He ended up requiring constant healing from the bard and ranger to keep him from drowning permanently.
5 – Mirrors of polished stone line the cavern’s walls. There is something unusual about the reflections.
A web of interwoven tunnels forms a room, of sorts. The floor and walls seem natural, save for a multitude of sections of smooth, polished, black stone. There is no volcanic activity in the area, so the presence of obsidian is strange to the party. But there is something far stranger. It takes them a moment to notice, while gazing into the clear reflections, that the other side is… delayed. The reflections follow their movements and actions but only a fraction of a second after the real articles. This discovery is instantly disconcerting. Their spine’s chilled, the party turns to make a hasty exit. Behind them, the reflections stop their mimicry.
Inspired by a dungeon encounter featured in Critical Role, this encounter makes great use of a sudden stomach-dropping moment. The players will come across the strange room and hopefully begin investigating. Let them look around and do as they wish. You want them to have them spend a little while in view of the mirrors before they notice the delay, which itself might require a high perception. This also makes this room a fantastic entrance for a dungeon, needing the players to search for the doorway or a way to open it. A great and chilling way to use this without a dungeon is by having both tunnels into the room collapsed. Players will need to move the rubble to make it through. Once the encounter begins to unravel, they will hopefully realize why the previous visitor tried to seal it away.
From here you are free to use Matt Mercer’s doppelganger-esque monsters, but we have our own approach. When your players touch or collectively move away from the mirrors, have the reflections begin to act. They can reach out of the obsidian, their form crudely comprised of the stone and somehow constantly reflecting the person they resembled. Statblock-wise, you can use a flesh golem with a number of hit dice to match the player (average 8.5 x player level, rounded down). Remove its Berserk, Aversion to Fire, and Lightning Absorption, but raise its AC to around 14, depending on party level and size. Knock its weapon immunity down to a resistance. Keep in mind that there should be more than one of these, so you may wish to scale them down. Finally, you can also add a vulnerability to thunder damage.
The reflections’ special ability will come from their nature as copies. Make notes of any weapon, attack, ability, spell, or even tactic that a player uses and have their reflection copy it after seeing it. Your players should notice this quickly and adjust to account for it. New copies should appear slowly, perhaps swapping out when an active reflection retreats back into the mirrors to reposition. They can then reemerge from a different mirror. If you wish to give the creatures a goal, have them attempt to drag players through the obsidian and into a dark, crystalline mirror of the room. These players will then make constitution saves to fight slow petrification that resembles them becoming one of the creatures.
6 – The party drops into a tunnel that seems to travel in a wide loop.
Following the path down a slope, the adventurers drop through the ceiling into another tunnel. It runs in both directions, curving into darkness. They choose one that runs in their general heading and continue walking. This new tunnel follows a gradual right turn that maintains as they follow it. It is only after an hour or so of turning right that the travelers begin to question their circumstance and investigate, finding rock formations that they could swear they have already passed. Yet, the opening they entered from is nowhere to be seen. Has something trapped them in a loop?
The most important aspect of running this encounter is understanding the reasoning behind it. Fortunately, it’s quite simple. A group of kobolds, short on resources, has set up a tunnel that runs in a wide circle. They watch for anyone that drops into the trap, sealing the entryway once their prey is far enough away. The trappers are then able to watch on from smaller tunnels as their victims ‘travel’, slowly growing weary. Eventually, they will die of exhaustion, starvation, or dehydration. That’s the kobolds’ plan, at least.
Running this cave encounter is quite simple and comes down to your descriptions. For a start, your players need a reason for being in the cave. This is easy if they are spelunking, as the descent can just be the natural progression of their path. If they are following a tunnel road, however, you might have a voice call for help from a side tunnel. The echo would beg for anyone nearby to free it from a collapse. This is another kobold trick. It can draw players into the trap and even continue to call, constantly just ahead of them, to keep them moving.
Once your players are in the loop, the kobolds will let them walk away before sealing the entrance. This could be done magically or with a fake section of stone that they slide over the hole. A perceptive player might hear this movement behind them, which is good. Your players will be ready for an ambush and expect the reality even less. Your description comes next. Describe random, small features as they move and, most importantly, do not place verbal emphasis on the curve of the tunnel. Our advice would be to write a list of five minor features, such as a grouping of stalactites or a pile of mossy stones. Slowly incorporate them, in order, as the party travels. Let the characters speak in between and simulate the passage of time. Once the list is done, repeat it and see if your players notice.
Eventually, a party member will catch on, hopefully from a player recognizing the pattern. If you find your table being unobservant or not realizing, feel free to give the most perceptive character a nudge. Start with a, “something is odd about this section of cave,” in the location of one of your repeated features. If they still don’t get it, progress to, “it feels… familiar?” Escape should then be relatively simple. They can quite easily navigate back to where they entered and find the opening with some investigation, or a perception check might expose kobold movements nearby. The kobolds will not attack if the party finds them, so some quick negotiation or (more likely) intimidation can have them reveal their plan and the exit.
7 – A living colossus is being carved by faithful undead and it wants the party to join their ranks.
Many centuries ago, a small cult sought to carve a body for their god. Their ambitions drew attention, however, and they were dealt with after making only minor progress. But the will of their master would not be halted and it raised them to continue their work. Unfortunately, it overestimated the strength and work ethic of animated corpses. They have toiled away at their task since then, slowly chipping away a set of shoulders and a chest. The party, drawn by the sounds of tools, are the first visitors they have had in some time. This delights the colossus, which seeks to exert its will over them and have the adventurers aid in its construction.
This cave encounter is one that can be played for humor or danger with very little adjustment. It will begin with the players either stumbling across the chambers or being drawn by the echoes of what they believe to be regular miners. When they arrive, the undead will face them and block the exit, but not attack. This is when the voice of the colossus can manifest. It should as prideful and commanding as any other god, projecting its words into the players’ minds and demanding fealty. Of course, it has only been carved down to the elbows and is not fully animate, so it cannot actually act against them.
This is when you will need to choose the tone of your cave encounter. We feel it’s safe to assume that your players will say no to the giant stone head. Its response will be the determining factor. For humor, have it grow increasingly desperate as they deny its requests, eventually to the point of begging. It thought the undead would be a good idea but they’re so slow and weak that it will take a millennia before the being is free. You can display this if the zombies and skeletons (and their variants) attack by having each one fall with a single attack. The voice can progress from threats to bargains. It can even ask the party to take a section of stone that it places itself in, seeing that as a better alternative.
Making the encounter dangerous is a different kind of fun. This version will see the colossus grow angrier and more domineering as it seeks to simply add to its faithful. It will command its legion to attack, which should have greater numbers and variations than the previous example. While the players fight, the colossus itself can attempt to charm them. You can have this act as a stacking effect, with the first failure (of a wisdom save) charming them until the end of its next turn. A player that fails the save while already charmed (or by five or more?) can then be subjected to a Command with the added option of being forced to attack a creature of the colossus’ choosing.
Players can win this version of the fight by killing the legion and leaving, thereby halting the excavation, or by attacking the stone head. Simply set a damage threshold at which the colossus’ core is exposed. It can appear as a gem or other relic, deep in the stone. Removing this object will isolate the consciousness in it and limit its powers to telepathic speech. The party can then find a way to safely destroy it, keep it, or later sell it to an impressionable merchant.
8 – The party stumbles into the lair of creatures with control of the stone itself.
Continuing through their tunnel path brings the adventuring band to a disturbing sight. Flashes of variation in the stone are revealed to be bone, mostly bestial but some humanoid. They are absorbed into the cave walls, the stone melded into their form and arms outstretched as if clawing for freedom. It is a sickening sight, but thankfully temporary. The tunnel contracts soon after and no more bones are visible. But when the party later rests, the truth becomes more clear. A shifting of earth awakens them to see that the walls have constricted, the tunnel itself closed just beyond the range of their light. Within the stone, creatures are preparing to strike.
This introduction is similar to our first cave encounter but the combat it leads to is very different. Ideally, it will occur an hour or so before the players need to rest. You will begin with them seeing odd pieces of stone, which a high passive skill in perception, nature, or medicine might identify as unnatural. Looking closer can quickly show it to be bone. This serves to put your players on edge and raise the perceived stakes of the combat that comes later. Make note of the skeletons’ positions and the fact that they have been swallowed by the stone. It is likely that your players will expect an encounter from this, leading to them being on guard and traveling further before resting.
Ideally, the party will be eased slightly by passing beyond the bone formations. If one or more of them realize why this is, as the tunnel ahead shrinks, there’s a good chance they will increase their pace and push past the ambush. Good for them! Even if your creatures now panic to cut off their escape, your players are still rewarded for figuring out the enemy’s tactics. If they don’t, have them reach the point of needing to rest shortly after. They can set camp, place defenses, and work out a watch rotation, all of which may help in the next phase.
Your creatures will have been watching the players and will act out of sight. They will cut off a stationary party’s escape by closing the tunnel on either side of them (though this can be broken through) before constricting the rest of the chamber. A player on watch may hear this as the stone moves, again allowing them to act before being fully trapped. Once the characters discover them or the paths are closed, your creatures can attack.
The basis for our creatures is the earth elemental. While you are free to use the elemental as it is, we find it better to transfer its key ability to weaker creatures, letting us use a larger number. Both gargoyles and grimlocks are fun choices with different flavors. All you need to do is give them the elemental’s Earth Glide ability, with some visual descriptors to show this mutation. You can also give them custom ability ‘Shape Earth’ as a lair action. This will allow them to slowly modify the battlefield as the encounter continues, pressuring players to act quickly. The implication is that the stone can swallow them like the previous skeletons, though it is up to you if you use this as a real possibility.
Shape Earth. While using Earth Glide, the creature shapes the stone around it. The earth in the creature’s space draws on nearby material to expand and fill 5 feet in every direction.
9 – A raging monster threatens to crumble the cavern’s supports.
The creature’s speed, even at a full charge, was no match for the dextrous monk. She leaped over its head, spinning in the air to watch it pass under her. Her eyes, focused on her opponent as she now lands, track its path directly into the natural supports of the cavern. The beast’s momentum carries it right through the pillar, shattering stone in every direction and sending an uneasy rumbling along the floor and ceiling. Large chunks of stone fall in the vicinity, nearly crushing her and her party. They quickly realize that the monster’s horns are not the only danger here.
Let’s start with the real trouble of this cave encounter: introducing it. Creating an interesting combat scenario is all well and good but you still need to find a way to make it feel organic and fitting. We have a few options here. You can use this as the entrance to a dungeon or other protected location, awakened by a failed attempt to force the door open. Just keep in mind that this defense could collapse the entire entrance, so it makes the most sense to be guarding someone who can tunnel their way back out. Or perhaps it leads to a dungeon full of other trials that protect a powerful item? Maybe they are guards to a magical prison?
If you wish to use this as a random or independent encounter, place a lure for players. The creature might start off as a statue with a large, expensive jewel set in its forehead. Attempting to remove or tamper with this could then animate the statue. In this case, you can have the party contracted to find the jewel or have them come across it as they travel. An accompanying character could approach it or offer to pay for its retrieval. You could also just let your party’s greed take hold as dollar signs fill their eyes. This allows you to have the chamber appear randomly along their path, perhaps in the ruins of a long-destroyed dungeon chamber. You can simply hint at a story without needing to fully explain or tie it to other events.
The choice of creature for this cave encounter is relatively simple and boils down to using the (Trampling) Charge ability. You could use a giant boar or giant elk, but perhaps the best option is the gorgon. Its physical makeup is perfect for the setting and its abilities are exactly what we need. You can even remove its petrifying breath if you wish to avoid the risk, as the crumbling pillars help compensate for a lack of mechanical depth. If you want to replace it and focus on the encounter’s gimmick, allow the beast to dash as part of its charge.
Your combat arena should be an expansive room, dotted with at least a dozen pillars or support columns. Have each one be roughly ten feet from the next. These will first seem like options for cover, stealth, and movement for players, but they will quickly realize the hazard. Put simply, the monster will charge at players with no regard for the pillars. If its Charge causes it to pass through or continue into one of them, the column will shatter. Have anyone within five or ten feet of the column make a dexterity save to avoid the falling stone. Success will halve the damage, while failure will hurt them and render them prone. Failing by five or more can restrain them under heavy rubble.
10 – A group of Duergar explorers breaks through the cave wall, stunned to discover real surface-dwellers.
The first alarm was the sound of nearby stone breaking away. Soon enough, the party identifies it as the echoes as pickaxes and humanoid movement, just beyond one of the cave walls. Speech accompanies it. It is not long before the stone gives way in a small window, before more tools strike through to connect the tunnels. A group of Duergar steps through, clad in pelts of subterranean creatures and carrying supplies for an extended expedition. They stare in awe of the adventurers’ very existence. What the party does not realize is that these Duergar are from a secluded community, raised in the traditional teachings of the ‘myth’ of the surface world.
This cave encounter functions as a unique interaction that poses non-combat challenges. The Duergar are not hostile and would actually prefer to speak with and study the players, but there is an immediate language barrier. They will speak an odd dialect of undercommon so even a linguistically talented character will only understand broken pieces of speech. Otherwise, it is up to players to find ways to communicate. The party has the choice not to, of course, but the encounter’s context and any prior knowledge of Duergar should suggest that they could have useful information. And who knows, the enraptured locals might follow a group that ignores them.
Of course, the most important aspect of this cave encounter is the Duergar themselves. The gimmick here is that this group is from a long-reclusive community with no real connection to any larger society. This was originally due to them following the teachings of a specific god or creature. In planning, it allows you to disconnect them from other Duergar and focus on a unique identity. Their teachings have mutated and corrupted over time. They now resemble a cult, with a widespread acceptance that the surface world is a myth. But there has recently arisen a group of curious, excited, and brave explorers who have set out to prove this history wrong! This is the party that your players encounter.
The result of your encounter can differ depending on what your players value. At its simplest, let it function as a humorous interaction with a somewhat silly group of locals. Give players a breather between travel and combat. Have the dwarves show them sketches they drew from rumors of what humans look like by taking three general descriptors (like their height or limb length) and exaggerating them. Do the same for animals, trees, landscapes, and anything else the dwarves have never seen. You can reward players that take the time to speak with and understand them with knowledge of nearby dangers, directions that aid in their goal, or perhaps an item that combats a common problem in the caves. An antidote for petrification is a good example, especially for Encounter 1.
That does it for the first half of our cave encounters. We already have the second article in production to complete the set, after which will be a guide on running everything subterranean. In the meantime, let us know what you think! We love getting feedback to help us improve in the future. What did you think of our encounters? What other fun adventures have you run in caves, tunnels, or the Underdark? Feel free to comment below.
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