Introduction

Hall of the Crystal King is a 3-4 hour adventure for 5th-level characters set within the Crystal Tunnels map. It’s a puzzle-forward dungeon crawl about a dwarven king who loved his people, then loved his crystals more. The dungeon teaches the players what his clan once valued, then asks them to use it to open doors, to win a princess’s trust, and, if they’ve been paying attention, to put him to rest instead of merely killing him.

The adventure runs well in a single session. If you need a break point, the Last Campfire (Area 4) is a natural place to split the adventure into two shorter sessions.

Running The Adventure

This dungeon rewards attention. The four tenets of clan Deephollow; metal, mountain, crystal, and kin appear in The Forge (Area 3), are twisted on the Tormented Obelisk (Area 4), and decide the outcome of the encounters with Princess Dagny (Area 6) and the king himself (Area 9). Players who learn the tenets earn easier checks, a tamed blade, and a better ending. Players who smash and grab earn curses, skeletons, and a wraith.

Every polished crystal surface in this dungeon is a chance to show the players something: themselves, a half-second delayed, a stranger’s silhouette, or the king, watching.

Adventure Background

Generations ago, the dwarves of clan Deephollow watched a crystal fall from the sky. They dug it from its crater, carried it into the mountain, and built their hall around it. The crystal made them rich. Prospectors paid fortunes for shards of star-glass, and King Morgran Deephollow was, for a time, the most generous king the mountain had known.

The Corruption. Something lives inside the fallen crystal, an alien intelligence with no name in any dwarven tongue. It whispered to Morgran, and the whispers became hunger. The king began buying crystals, then seizing them, then sending expeditions across the realm to bring every shard home to him. He sealed his hall, turned his tenets into locks, and died on his throne with his hand on his hammer. When anyone touches what is his, he rises.

The Princess. Morgran’s only child, Princess Dagny Deephollow, resisted the crystal’s whispers. She forged a blade she believed could put her father to rest, but the corruption in the crystal bled into the steel, and she died before she could temper it with the values of her clan. Her spirit lingers behind the waterfall, grieving, still holding the sword.

The Entity. With the king’s body spent, the intelligence in the crystal needs a new host to continue gathering its scattered shards. It manifests as a guardian of living crystal in the Crystal Chamber (Area 5), and it is willing to bargain.

Adventure Hooks

Use any of the following adventure hooks to help tie the party’s backstory together, or inspire plot points to lead into exploring this dungeon.

Key NPCs

King Morgran Deephollow

Role: Former king of clan Deephollow, unrestfully sits on his throne.

Appearance: A dwarven corpse fused with jagged crystal protruding from the bone, beard threaded with shards, one hand grasping his hammer.

Personality: Possessive beyond reason.

Motivation: Everything that is his has been tainted by the entity. He must make sure nothing leaves to avoid the entity spreading its grasp on the realm.

Princess Dagny Deephollow

Role: The king’s daughter, currently a spirit hidden behind a waterfall.

Appearance: A dwarven woman lay on a crystal bier, wearing a belt of dwarvenkind, hands folded over a greatsword.

Personality: Weary, watchful, immune to her father’s corruption.

Motivation: Rest. For her father first, then for herself.

The Entity

Role: The intelligence inside the fallen crystal.

Appearance: A construct of living crystal; something vast glimpsed in refraction behind it.

Personality: Patient, alien, transactional.

Motivation: New hosts to gather their crystals so that they may reform to claim the realm as their own.

The Dungeon

The dungeon was once the hall of a dwarf king who went mad collecting crystals found scattered across the realm. In his madness, he restructured it into a tomb to keep all things he treasured interred with him, and to hide as much of the alien crystal away as he possibly could. His throne is locked behind a chain of traps and trials–built to deter thieves, or to lure the worthy to meet the king himself. Characters enter by rope through the ceiling of King’s Twins (Area 1) and work west and north toward the King’s Domain(Area 4), where bridges span the Crystal Depths to the Mad King’s Throne (Area 9).

General Features

Light. Crystal formations shed dim blue light throughout the dungeon. Where the crystals have been harvested or shattered, the tunnels are dark.

Sound. A low resonance hums through the stone, rising in pitch near large formations. Characters who listen at doors hear the hum before anything else.

Doors. Stone slabs veined with crystal, balanced to swing silently. Locked doors are noted in their areas and cannot be forced without waking something.

Reflections. Polished crystal reflects more than it should: other explorers who came before, the party a moment out of step, or the king watching from afar.

Alcoves. Crystal-encased skeletons rest in alcoves throughout the dungeon. Not all are so peacefully at rest.

Crystal Depths. A character who falls into the massive shaft spanning Areas 4 to 10 lands on a crystal pillar 1d8 × 10 feet below, taking 1d6 bludgeoning damage per 10 feet fallen.

Random Encounters

Random Treasure

1. King’s Twins

You descend by rope through a break in the ceiling into a burial chamber lit by crystal-blue braziers. A long pool of still water runs down the room’s centre. Two stone coffins flank it, identical down to the folded hands of the dwarves carved on their lids, with final offerings at their base. To the west, a sealed stone door waits. Two names are chiselled deep into its crown BROM and BRAM, and beneath each name a shallow stone basin waits, empty.

The east entrance is nothing but debris. The west door may be unlocked with a successful DC 17 Dexterity (Sleight of Hand) check or forced open with a DC 20 Strength (Athletics) check. Opening the door causes 1d6 crystal skeletons to rise from nearby alcoves.

The Puzzle Door. The door has no keyhole to pick and no seam to pry. Beneath each brother’s name sits an offering basin. The door opens only when each brother has been given the right three gifts in the right basin. There is no penalty for honest guessing.

The Twins. The coffins belong to Brom and Bram Deephollow, the king’s youngest sons, identical twins who spent their lives swapping places to trick the court, and set one last trick before the tomb was sealed. Six objects sit in the room, three offerings for each brother. But they were arranged to mislead, and have been rearranged by previous failed attempts to enter the dungeon. Only the script carved on each coffin tells the truth about who each gift belongs to.

The Offerings.

Each gift is easily interchangeable unless the carved epitaphs are carefully read. When the sixth correct gift settles into place, the west door grinds open.

Opening the Coffins. The contents inside the coffins are not part of the puzzle, and disturbing them is desecration. A character who pries one open finds a mummified dwarf and no way to tell which twin it is. Cracking a coffin wakes three crystal skeletons.

The Urn. A decorative urn stands on a pressure plate in the northeast corner; a successful DC 18 Wisdom (Perception) check reveals the plate. Characters can open the door to the Secret Hoard (Area 8) by filling the urn with the right amount of water from the pool with a successful DC 18 Dexterity (Sleight of Hand) check. On a failure, too much water has been poured, the urn cracks, and all the water in the room rises as a water elemental and attacks. When the elemental is slain, the water in the room evaporates.

The Pool. The entire base of the pool is a depressed pressure plate while it is filled with water. If the pool is emptied, the pressure plate lifts, opening the door to the Tilting Bridge (Area 2).

2. Tilting Bridge

Six crystal panels span a black pit, each one balanced on a central iron spine. Cold air rises from below.

Crossing. The bridge punishes imbalance. Characters must cross in pairs, one on each side of the spine. At each panel, both players secretly choose a face of a d4 and reveal at the same time (if you’re playing online, write a number from 1 to 4 and reveal on camera). If the numbers differ, their weight offsets and they advance to the next panel. If the numbers match, the panel tips: each character must succeed on a DC 15 Dexterity saving throw or slide off into the Cold Plunge below. If you’re feeling vanilla, skip the dice: two characters at a time cross with a successful DC 15 Dexterity (Acrobatics) check.

Cold Plunge. The pit is 30 feet deep and filled with 20 feet of freezing water (a water weird lurks here). A creature that falls in must succeed on a DC 15 Constitution saving throw or gain 1 level of exhaustion until it is dried and warmed during a short rest or through magic. A creature cannot gain more than 1 level of exhaustion from this pool.

Eye Statue. A crystal statue on the far side holds a gem in its socket that powers the bridge’s trap. If the gem is removed, the bridge solidifies into a single safe span, and two crystal skeletons wake in the nearby alcoves.

Skeletons. Encased in the crystal formation of one alcove skeleton is the key that unlocks the north door.

3. The Forge

Four stone reliefs of dwarven faces watch this room from its walls, each crowned with a different bronze fixture: a miner’s helm, a jewelled circlet, a hammer, and a tankard. Channels in the floor run from each relief to a cold central forge. Beside it sits an empty key mold.

The northern door is locked. The key must be forged.

The Four Tenets. Each relief honours a tenet of clan Deephollow. A character who succeeds on a DC 15 Intelligence (History) check knows them; otherwise, inscriptions beneath each face teach them:

• Metal. For mining, for war, for defence. The metal that carves the mountain and its jewels.
• Mountain. The earth itself, on which the dwarves live and are born.
• Crystal. The gems that made the clan rich and merry.
• Kin. The tenet of ale, family, and togetherness.

Forging the Key. Characters must melt the bronze fixture from each relief and re-cast it in the central forge as a symbol of its tenet, filling the key mould with what remains. A character proficient with blacksmith’s tools works with advantage and can guide the others. A character who simply pulls a fixture free is cursed (see the table below).

Curses. Each relief guards its tenet with a curse. Roll or choose based on which fixture was taken:

Curses persist until removed by a remove curse spell, or until the king is put to rest.

The Shortcut. Alternatively, a character who succeeds on a DC 15 Intelligence (History) check knows what these statues allude to in dwarven culture and may sacrifice their own material objects to feed the forge instead. The forge accepts the offering and casts the key, and 2d4 crystal skeletons rise from their alcoves. The clan does not approve of substitutes.

Secret Storage. A character who succeeds on a DC 15 Intelligence (Investigation) check knocks on the Mountain relief and hears a hollow cavity behind it. A successful DC 15 Strength (Athletics) check breaks the relief down, revealing 7 platinum pieces, a dwarven thrower, a potion of flying, and 2 potions of healing. A character that damages the relief is cursed (see table above).

4. King’s Domain

The tunnel opens onto a cavern that swallows your light. A colossal bloom of crystal rises from a shaft with no visible bottom, and on it sits a throne. Rope bridges stitch the dark between platforms of stone. On the nearest platform stand the ruins of a mining operation, a shattered obelisk, and a bronze lantern-stand bolted to the rock.

Tormented Obelisk. The obelisk lies in five carved chunks. Reassembling it requires a successful DC 15 Intelligence (Investigation) check, or no check at all from players who physically match the described break-lines. Once restored, its dwarvish inscription can be read aloud with four words gouged out by a chisel:

Metal serves no hand but the ______’s.
The mountain is not your mother. It is my ______.
The clan does not keep the crystal. The crystal keeps the ______.
Raise no tankard and sing no song until every shard is ______.

The missing words, in order: king, vault, clan, mine. A character who learned the tenets in Area 3 recognises this immediately for what it is: the four tenets of Deephollow, twisted into greed. Speaking the true tenets aloud before the obelisk (metal, mountain, crystal, kin) causes it to resonate.

The Lantern Device. A bronze contraption drilled into the floor accepts any light source. When lit, its beam bounces off nearby crystals before travelling through the obelisk while it resonates, causing a final beam to reveal a hidden button on the northern wall. A character cannot spot the button unless on a successful DC 20 Wisdom (Perception) check. Pushing it opens a hidden door.

The Last Campfire. Beyond the hidden door is the campsite of a previous explorer. The fire is on its last embers, and the stew smells hearty; the belongings suggest someone planning to return. Among them: a chime of opening, 2 days of rations, a bedroll, thieves’ tools, rope, and a scroll of mirror image. There is also a journal. It describes the secret room behind the waterfall, theories about what lies in the depths below, how the mad king rises when anyone touches what is his, and that the princess has become a grieving spirit longing for rest. If you’re using the Missing Spelunker hook, this camp belongs to the one they’re chasing.

Bridge. A classic broken bridge spans toward the far platforms. A character crossing by foot must succeed on a DC 13 Dexterity (Acrobatics) check or succumb to the Crystal Depths (see General Features). A successful DC 15 Wisdom (Perception) check while crossing the bridge spots Area 8.

5. Crystal Chamber

Jagged Pass. The tunnel into this chamber is riddled with sharp crystals. A Medium or larger creature traversing it must succeed on a DC 15 Dexterity (Acrobatics) check or take 2d4 slashing damage.

The chamber beyond is a geode turned inside out. Every surface refracts, reflecting shattered versions of yourself a hundred times, and in the largest formation, something reflects that isn’t you. A shape of facets and light unfolds from the crystal and regards you without eyes. Behind it, a wooden mine lift waits at the mouth of a mineshaft.

Crystal Guardian. The entity that corrupted the king manifests here as The Entity (Crystal Guardian form). With the king’s body at the boundary of usefulness besides the dungeon guardian, the crystal doesn’t have a host to gather its crystals across the realm, so the entity offers the characters its power should they offer their body and mind as a host.

A character who accepts it as a host gains one of the following boons of their choice after implanting a shard into the nape of their neck:

• Crystal Resilience. Gain 2d10 temporary hit points whenever they touch a crystal (once per short rest).
• Reflection Step. Use a bonus action to teleport to an unoccupied space within 5 feet of a crystal they can see within 30 feet.

If any character carries Princess Dagny‘s blade or her blessing from the Princess (Area 6), the Entity attacks immediately, knowing that Dagny interferes with the entity’s goals.

Mineshaft. The elevator still operates. It descends 300 feet past massive crystal spikes into the mining operation the king once ran to uncover and store more crystals. What lies deeper is beyond the scope of this adventure (see the Conclusion).

6. Princess Falls

The room behind the falls is easy to spot once the characters approach the waterfall.

Behind the curtain of water, a dwarven woman lies in state on a bier, untouched by time. A belt of gold links circles her waist. Her hands are folded over the hilt of a greatsword whose blade drinks the light.

Princess Dagny. The princess wears a belt of dwarvenkind and has been interred with the Sword of Wounding (Greatsword). The corruption that consumed her father never quite reached her, but it lives in the blade she forged to end him. Touching the sword wakes her.

Woken, she demands to know why they’ve come. The characters may convince her they are here to help with a successful DC 17 Charisma (Persuasion) check. She then offers the sword freely. A character who attunes to it gains the following flaw: “Those who wear crowns deserve to be hurt.”

Taming the Blade. Dagny explains that the sword must be imbued with the values of her clan before it can grant her father rest rather than merely destruction. She suggests using the forge to craft an attachment like a new hilt, sheath, or charm. The party may return to The Forge (Area 3) and attempt a group skill challenge, including a successful DC 15 Intelligence check with blacksmith’s tools, a DC 17 Strength (Athletics) check at the 

bellows, and a DC 16 Dexterity (Sleight of Hand) check for the finer details of craft. Success removes the sword’s flaw, turns the sword into a Defender Greatsword, and allows the king to be put to rest (see Area 9). Wounds the Defender Greatsword deals to the king cannot be regenerated.

By Force. If the characters try to take the sword by force, the princess’s spirit rises as a wraith accompanied by three will-o’-wisps. She fights to protect her home and her tomb.

7. Tools of the Mine

This strip of cliff connects to the central crystal platform. A decorative metal urn in an alcove depicts, in relief, the story of clan Deephollow finding a crystal that fell from the sky (refer to Adventure Background)

Mining tools cut from crystal lie among the wreckage of the operation. One functions as a Weapon of Warning (war pick).

A successful DC 17 Wisdom (Perception) check spots Area 8.

8. Secret Hoard

A small alcove holding additional treasure of the Crystal King: 121 cp, 202 sp, three sets of dwarven jewellery worth 20 gp each, a stone of good luck, a ring of jumping, and a rope of climbing.

A character who succeeds on a DC 18 Wisdom (Perception) check finds a hidden lever that opens a secret door back to the King’s Twin’s (Area 1).

9. The Mad King’s Throne

The throne crowns the crystal bloom itself. The remains of King Morgran Deephollow sit upon it. Crystal has grown through his beard, his crown, and the arm that rests on his hammer. At his feet, a chest strains at its hinges with star-glass.

The corpse of King Morgran Deephollow (The Crystal King) rests with a hand on his hammer. When a character touches his treasure chest or himself, he awakens and attacks to kill any intruders.

Tactics. The king opens by slamming his hammer into the crystal, showering the platform in shards. He uses the reflections to reposition, and his attacks prioritise whichever character carries the most crystals.

Roleplaying the King. The entity believes the king is well under its control, but his motivation is driven to protect the realm from succumbing to the crystal by keeping intruders out of his hall.

Putting Him to Rest. If the king is reduced to 0 hit points by the Defender Greatsword made from Dagny’s blade, read:

The crystal in his beard goes dark, vein by vein, like a hall of lamps being put out for the night. The king’s hand slips from his hammer, and then he is stone. The mountain falls quiet, and somewhere far below, something shrieks.

If he is destroyed by any other means, the crystals help him reform back on his throne in 24 hours.

Treasure. Morgran’s Fall, 210 gp, 103 pp, two diamonds worth 100 gp each, a platinum torc worth 20 pp, dwarven bracers worth 40 gp, a map of the realm showing dig sites where more crystal can be found, a map of a structure in the mines below that belongs to the crystal, a ring of feather falling, an immovable rod, and an elemental gem (earth elemental).

Conclusion

The king may rest, but the entity has not died. It retreats down through the crystal, into the mines the elevator serves, where the king’s map marks a structure that was never dwarven work. The dig-site map in his hoard points to more crystals scattered across the realm, each one a whisper waiting for an ear.

Will the characters leave and enjoy their plundered treasure, or will they see the end of this entity once and for all?

More 2MT content to inspire more adventure from this dungeon:

• Fallen Star Battlemap
• The Crystal Horde Adventure
• In Crystal Skies Adventure
• Through Crystal Eyes Adventure

Appendix

Appendix A: Statblocks

Appendix B: Magic Items

Morgran’s Fall (Warhammer)

(Very Rare, Requires Attunement)

Weapon – Warhammer – Martial Melee 1d8 (1d10) Bludgeoning – Properties: Versatile – Mastery: Push

King Morgran Deephollow raised his hall with this hammer and sealed it with the same. The first shard of the fallen crystal is set in its head, and it has never stopped whispering. He held it as a king, and clutched it as a corpse.

You gain a +2 bonus to attack and damage rolls made with this magic weapon. On a hit, the target takes an extra 1d8 cold damage.

Treasure Sense. While holding the hammer, you know the location of any crystal or gemstone within 30 feet of you.

Shard Slam. As an action, you can slam the hammer into the ground. Each creature within 10 feet of you must make a DC 15 Dexterity saving throw, taking 3d6 slashing damage on a failed save, or half as much damage on a successful one. The area becomes difficult terrain until the start of your next turn. Once used, this property can’t be used until the attuned creature gains the benefits of a long rest. 

King’s Curse. This weapon is cursed, and becoming attuned to it extends the curse to you. Until the curse is broken with a remove curse spell or similar magic, you are unwilling to part with the hammer, keeping it within reach at all times. You also gain the following flaw: “It’s not fair for anyone to be consumed by greed, so I take away whatever makes them greedy.”

When you finish a long rest, if you have not added a new crystal or gemstone to your possessions since your previous long rest, you gain no benefits from that rest.

Appendix C: Adapting Other Map Variants

Mo has made some beautiful variants to this dungeon that stretch its uses far. Here are some suggestions if another variant is better suited to your campaign.

Lava. Swap the Cold Plunge for a magma pool (fire damage, no exhaustion), reflavour crystal skeletons as obsidian, and make the entity a burning intelligence that fell as a cinder, not a star. The king hoards fire opals.

Celestial. The crystal fell as a fragment of something divine. Radiant damage throughout, will-o’-wisps become guiding lights, and the entity presents itself as an angel, which makes its offer of a host far more uncomfortable. This is a great variant to use an overgrowth of plant monsters that serve a vibrant lifeforce.

Space. Lean into the alien. Low gravity in the Crystal Depths (halve fall damage, double jump distances), the hum becomes a signal, and the structure in the mines below is unmistakably a vessel. Perhaps this one shifts between dimensions and randomly changes to different variants?

Appendix D: Dungeon Soundtrack

I like to find music to write my adventures to. Sometimes it’s contemporary; this time it’s instrumental ambience. Here’s a background playlist to accompany raconteurs telling the story of the brave who venture into the crystal depths. Listen to it while you prepare the adventure, or play it during your session between combat encounters as the characters explore the dungeon.

Listen: Hall of the Crystal King on Spotify (9 tracks, 38 min)

Appendix E: Additional Tokens

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Credits

• Maps, scene art, handouts, and royal token art by Morgan Pabst (Mo the Half)
• Hall of the Crystal King adventure by Ian Arguilles
• Additional token art by Fairbanks
• Post-processing and formatting by Ross McConnell

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