Updated: Mar 19, 2021
Written by: Nicholas Uster
This one-shot adventure is designed for a party of 2-4 5th level adventurers. It will take up to 3 hours to complete. All underlined creatures, people, or items are linked. Click on their name to pull up their stat block or other information!
The party is hunting for the legendary Ring of Sapphire, rumored to be deep within this dungeon. Known as the Crystalline Caverns, this ancient cave system was dug by a guild of Kobolds. It is said to contain priceless relics left behind by its old inhabitants. With great rewards come great risks, as legend tells of a Sapphire Dragon that prowls the caves.
If you’d like to add some more background to the story, answer some of these questions:
How did the party meet or come to know each other? Are they all part of a guild, association, creed, etc? Did they meet in a tavern?
How did the party find out about this treasure/adventure/location? Did someone tell them? Did another adventure lead them here? Did they see it in a dream?
What is so special about this treasure/adventure/location? What gives it importance? Why should the party be interested?
What about this treasure/adventure/location creates tension for the party? Is there danger involved? What are the risks? What keeps the party in suspense?
Environmental Hazard: Crystalline Sludge
A strange slow-flowing sapphire-colored slush oozes from cracks in the cavern walls, it has a faint glow from small quartz crystals suspended within it. If a player contacts the sludge they have to make a constitution saving throw, rolling a 15 or greater. On a failure, the DM chooses one of two things to happen.
1. The toxic vapors rising off the sludge burn the player’s skin, dealing 2d6 acid damage.
2. The sludge turns solid and the player is grappled and must break free of the ice to be released. If the player attacks the ice with a weapon it has an armor class of 11 and 6 hit points. If they make a strength check to escape they must roll an 11 or greater.
Entering The Dungeon (Room 1)
DM notes: The party begins at the entrance of the dungeon, having just rappelled down a deep crater within the icy caves. Just as they reach the ground, their rope falls, having detached from above.
Describe to the party what they see: “You see a 15-foot high cavern entrance dimly illuminated by the glow of green quartz crystals embedded within the icy walls. A slow-flowing sapphire-colored slush oozes from cracks in the ceiling and collects in large puddles on the floor, it has a faint glow from small quartz crystals suspended within it. Ahead of you is a 30-foot long hallway carved within the ice. You can see your reflection in a *mirror-like wall of ice at the end of the hallway. Diverging from the hallway are two dimly lit channels.”
*If they perceive the mirror they will see the name “Dhalmass” in its reflection, and carved on the ceiling of the hallway is that name spelled backward (ssamlahD).
*If they perceive the hallway leading to room two, they may hear labored breathing or moaning.
*If they perceive the hallway leading to room three they may hear heavy beast-like breathing or see claw marks that have scraped the ice.
The Puzzle Of Three Souls (Room 2)
Describe to the party what they see: “Inside the room are three pillars of ice, each with the ghostly visage of a person frozen inside. Only their faces and chests are exposed, where it seems their heart would lie. There is a sharp icicle laying on an altar on the opposite wall of the room.”
DM notes: Each being has been trapped here, all will beg to be freed and claim that the other two must be killed. The players can use the icicle that has been provided or a weapon they have on hand. Any attacks made against the beings will automatically hit and will kill them, and they will turn to dust. The final being that remains will give the party a boon or a bane and then fade away as their spirit is freed.
Being 1: Arthos Ember, human fighter. Claims to be the past owner of the Ring of Sapphire. Will give the party information about the Sapphire Dragon at the end of the dungeon if they are freed. Once freed, Arthos will warn them about its immunity to cold damage and its cold breath attack.
Being 2: Renwick, Dragonborn Paladin. Tried to “destroy the evil within this tomb.” Soon found themselves imprisoned here. Renwick keeps repeating “it consumes all, your armor means nothing, it must be destroyed.” Once freed, they will warn the party about the Gelatinous cube in room 5, and their ghost may even shield the players from its attacks if they fight it (at DM’s discretion).
Being 3: Glibby, Bullywug wizard. Glibby should seem very goofy and harmless to the party. They came down here for a crystal to use in one of their spells. Claims they will give the party a magical item if they are freed. They are secretly a trickster demon. Once freed, they will shed their disguise, revealing a long barbed tail, and will stab a party member. The party member will be poisoned for 1 hour.
Guardians Of The Relic (Room 3)
Describe to the party what they see: “You see a square room roughly 30 feet wide and 15 feet high. As you step inside you notice the thin ice floor has the sludge from the dungeon entrance flowing beneath it. There are small holes in the ice that seem to have already cracked and fallen into the sludge. Towards the back of the room (on much more solid ground) are two sleeping wolf-like beasts. One wears a Ruby key tied to its neck with a heavy steel collar. The other wears a Sapphire key tied to its neck with the same collar.”
DM notes: The beast with the Ruby key tied to its neck is a Death dog and the beast wearing a Sapphire key is a Winter Wolf. The beasts are not-necessarily hostile, and the party can try and talk to them by making an animal handling check and rolling an 18 or greater. If they are not succeeding and keep trying, the more they try, the more angered the beasts become. If the players use the dog treats from the barracks or a similar option, the dogs will likely yield their keys. Players can also take the keys by making a stealth check and rolling a 16 or greater.
Once the party enters the room, if the players move on their turns, they will have to make dexterity checks and roll an 11 or greater to make sure they don’t step on weak ice. If they do, their foot breaks through the ice, and the effects of touching the Crystalline Sludge are applied.
The Magic Mirror (Room 4)
Describe to the party what they see: “To enter this room you walk down an icy ledge. You enter through the side of the room. As you turn to your right, you see the room is roughly 15 feet long but 30 feet high. At the end of the room is a grand mirror-like wall of ice that allows you all to see your reflections. However, your faces seem blurred. The mirror reflects you and the large ice wall behind you. Laying on the floor is a longsword that has been shattered, with the hilt and the broken blade laying on the ice.”
DM notes: *If the party makes a perception check on the wall or rolls high in a regular perception check, they notice the withered remnants of something carved on the back wall across from the mirror (just like the mirror at the dungeon entrance).
The players must carve their names backward in the wall so that it reads normal in the mirror. They can use the remnants of the sword on the ground or anything they have on hand to carve. Once a player’s name is correctly carved the mirrored wall will seem to have disappeared and they will then be able to see that it is just a big opening in the wall. If the players attack the mirror, they are dealt whatever damage they deal to the mirror.
In the empty opening are three identical Kobolds sitting on the ground, each with a manacle (handcuff) clasped to one hand, with the other side of the manacle open. The one in the middle is actually wearing a Cloak of Mirror Image, which gives the wearer the effects of casting mirror image on themselves for 24 hours. The other two are illusions from the spell. This Kobold has been trapped in here for decades but the magic would not allow him to die. His mind has deteriorated and he will attempt to cuff himself to a party member so that he can not be left behind. If he successfully cuffs himself to a party member they must make a strength check or check with thieves tools to open the clasp, rolling an 11 or greater. If the party tries to talk to him he will mention that someone scratched his name out on the wall, trapping him within the mirror. If he tries to leave the mirror, the magic wears off and he turns to dust, leaving behind the cloak for a party member to use. If the party kills him, then the same thing happens.
A “Grate” Time (Room 5)
Describe to the party what they see: “The room is a 30-foot square and about 15 feet tall. The left wall has shattered shelves, nearly empty, which seem to have once held rations. The right wall has rotting wooden pegs nailed into the wall that barely hold up a canvas bag. One wall has an iron chest sunken into the wall and a small entrance carved out to enter the barracks (Room 6). In the center of the room is a grate 10 feet in diameter over a hole that is 30 feet deep. Steam emerges from the grate and gives off the only warmth found in the caves. Clutching the grate are freezer-burned bony hands from past souls. Pitons hold the grate down.”
DM notes: The canvas bag contains climbing equipment: a 50-foot rope, a pair of boots with iron spikes that give the wearer a climbing speed of 30 feet on ice, a small oil torch with oil, and pitons. The iron chest has 2 slots, each matching the Ruby and Sapphire keys hanging from the dog’s necks in room 3. The keys must be inserted and turned at the same time for the chest to open.
Inside of the chest is a Blade of Hellfire. If a party member takes it, describe to them what it does: “This item appears to be a longsword hilt. While grasping the hilt, you can use a bonus action to cause a blade of pure fire to spring into existence, or make the blade disappear. While the blade exists, this magic longsword has the finesse property. You are proficient with the blade. You gain a +2 bonus to attack and damage rolls made with this weapon, which deals fire damage instead of slashing damage.”
If the players look in the grate they see an empty steamy icy cavern. Sitting at the bottom of the hole is secretly a Gelatinous cube (with the corrode metal trait) that the troops would throw prisoners or items in to have them destroyed. The cube has the transparent trait as explained in its stat block, so even when the cube is in plain sight, it takes a successful perception check (rolling a 15 or greater) to spot a cube that has neither moved nor attacked. A player that tries to enter the cube's space while unaware of the cube is surprised by the cube.
Corrode Metal: Any nonmagical weapon made of metal that hits the ooze corrodes. After dealing damage, the weapon takes a permanent and cumulative -1 penalty to damage rolls. If its penalty drops to -5, the weapon is destroyed. Nonmagical ammunition made of metal that hits the ooze is destroyed after dealing damage. The ooze can eat through 2-inch-thick, nonmagical metal in 1 round.
At the bottom of the pit, under the cube, is an Ioun stone (it was unable to be damaged by the cube) which provides the holder advantage on all constitution checks/saving throws and allows the wielder to cast Fire Shield once per long rest. Also at the bottom are the decaying remains of Renwick from room 2.
The players must fight the cube and kill it to obtain the stone, once the cube is killed it will turn to lifeless liquid. The players can also obtain the stone by using a spell or some creativity to avoid fighting it.
The Barracks (Room 6)
Describe to the party what they see: “The room is a 15-foot square that is 15 feet tall. There are uniform canvas-covered ice blocks and some small storage chests/barrels. On a shotty table in the center of the room is a chessboard with only one remaining piece, a bishop crafted from the same quartz found on the walls. Across the room is a small opening that seems to lead into a dark hallway (this goes to room 7).”
DM notes: If the players examine the chess piece with an arcana check and roll a 10 or greater, they will realize it is magical. The chess piece summons a priest to heal a player that has fallen to 0 hit points. It will restore them to consciousness with 1 hit point. Scattered amongst the chests are a few trinkets. A letter from a kobold minion describes what horrors the ring of sapphire brought about. There are two healing potions that restore 2d6 hit points. There are also dog treats, which are dried animal bones.
The dark hallway that leaves room 6 is a long, empty hallway that is eerily quiet. All the players can see is a dim light at the end, flickering from the next room.
The Sapphire Dragon (Room 7)
Describe to the party what they see: “You see a 50-foot square room that is 30 feet high. Grand quartz shards hang from the ceiling, dripping with a familiar sapphire-colored slush. Monumental pillars of ice in the corners of the chamber are shattered and the ceiling dips in on a slight tilt. Across the room is a large altar with a throne of ice once fit for a king, but it lays broken with dark red blood spilled across the luxurious furs adorning the ground. The carcass of what was once a former adventurer is being gnawed on by a colossal Sapphire Dragon. As it bears its teeth, you can see the Ring of Sapphire shine, imbedded in the side of one of its jagged teeth.”
DM notes: The floor of this room is extremely slippery, and anytime a player without spiked boots tries to move, they must make a dexterity saving throw and roll at least a 10, or they will fall prone at the end of their turn.
This is the big fight! Have fun and give the players a challenge.