Kassoon

No Prep Module: Terror From The Deep for D&D or RPGs

This adventure can be can be easily customized to a party of any size or level, or run as a level 6 adventure for 5 players. It can work as a small side adventure in an existing campaign, as a standalone one-shot, or the start of a new adventure. Use the links to the tools in their relevant section to customize the adventure to your party.

Fairlun sits in the shadow of a large ruined castle, and is known for its mines and industry. The city is ruled by a half-orc priest of the local religion that keeps the rest of the populace under strict control.

Island Ruins

Fairlun has an interesting secret: every natural-born citizen is a sorcerer, their powers manifesting sometime around puberty. Assume most NPCs have at least 1 sorcerer level.

The PCs will learn firsthand the dangers of magical populace when, sometime during their exploration of the town, a house will erupt into a massive fire. You can have the PCs be inside when the fire starts, or be passing by, but within seconds the entire structure will be completely engulfed in flames. Citizens can be heard trapped inside screaming for help, as the beams collapse and bar the doors. The PCs will need to decide what to do, if/how they'll rescue the citizens while not succumbing to the flames themselves. Have the PCs decide on a course of action and make any relevant skill checks to progress, taking 2d10 fire damage on each failure. At least one citizen should be trapped behind a locked door.

Most people in town are either boarding up their homes, or leaving town entirely. If the PCs investigate they'll learn that every 10 years, during the longest night, an island supporting a seaweed covered ruin rises from the water. Terrible monsters emerge every night to terrorize the countryside before the island sinks back beneath the waves a week later.

There's a long-standing bounty on defeating the monsters that emerge and even one to clear the ruins once and for all. Many adventurers have traveled to the city to claim the bounty, though no one has ever managed to clear the ruins.

The island is covered in seaweed, barnacles, and other marine life. The entrance to the ruins is easy to find, still wet from years of flooding.

Dungeon Map

Enemy Patrol: 4 Deep Scion (CR 3: Volo's Guide to Monsters p. 135) [Hard, 2,800 XP rewarded] [Customize]

Chance of Encounter Per Rest: 15%

Room Contents

You can also generate different descriptions using the Description Generator. The dungeon starts in Room 19, with the finale in Room 1. Many of the rooms in this dungeon are still flooded or completely submerged underwater.

1

Water fills the room. The walls are lined with aged books and tomes, their leather covers faded and muddy through misuse. Life-sized scarecrows of elves line the passageway on both sides, their eyes seeming to follow you. Benches coated with algae lie about the floor in disordered anarchy. Seaweed strands fill the staircase, making it difficult to see even the ceiling. A skeletal figure dressed in burnished chain stands sagging at attention, holding a rusty war pick. An eel-like creature with a long body about 30 feet long floats in the water here, its tendrils wrapped around the half-eaten corpse of a monster. Its skin is a sickly shade of green with an orange-pink underbelly and a maw full of razor sharp teeth.

There are 1 Aboleth (CR 10: Monster Manual p. 13) [Hard, 5,900 XP rewarded] here. [Customize]

If the party hits the aboleth with an attack and it doesn’t kill it, it becomes immune to that attack.

The aboleth makes its lair within the ruins and is trapped any time the island rises. To survive, it enslaves and consumes any monsters (or people) that it finds within the ruins. The monsters, not wanting to be eaten, end up fleeing the ruins to wreak havoc upon the surface.

Aboleth

2

A stone-framed bed fitted with leather straps stands near a wall. The room contains two curtained alcoves as well as a larger area stuffed with wine barrels. The south end of this room has collapsed, exposing the room beyond. A short flight of stairs leads up to a massive, iron-bound door. A dirt-caked halfling skull is fixed to the center of the door by a steel spike.

There are 2 Four-Armed Gargoyle (CR 4: Fifth Edition Foes p. 113) [Medium, 2,200 XP rewarded] here. [Customize]

In the south passage is an unlocked door.

3

The ceiling here rises about 25 feet above, and coals and Sun-bleached bones coats the floor. Vines stretch between the totem that supports the concave ceiling of a grand, water-filled room dimly lit by flickering orbs in steel candelabras. A tight passageway leads to another small room after this one. Above a door in the northern wall is mounted the skull of a griffon.

There are 2 Eye of the Deep (CR 5: Monster Module p. 17) [Hard, 3,600 XP rewarded] here. [Customize]

4

A chiseled granite railing boxes in this lofty plateau, which oversees another room filled with water. You come to a dark landing 45 feet wide and 30 feet long. A tall, damp wardrobe relatively shaped like a coffin, its black doors painted with griffons, stands between four moist mirrors hanging on the south wall. A pair of leaded glass doors, their panes cracked and broken, stand open between panels of stained glass set into the east wall. These panels depict gargoyles. Directly across from the stained glass window stands a set of double doors in the south wall.

There are 2 Killer Whale (CR 3: Monster Manual p. 331), 1 Eye of the Deep (CR 5: Monster Module p. 17) [Hard, 3,200 XP rewarded] here. [Customize]

In the east passage is an unlocked door.

In the south passage is an unlocked door.

5

The floor is spread with excrement and Sun-bleached bones sitting below the water that fills it. A closed stone chest rests next to a wall, its lid chiseled with an emblem. Double doors of stone stand closed to the west. Slick scrolls and quills border the walls of this room. Summoning circles sit away from the double doors that give access to the room.

There are 2 Kelpie (CR 1: Fifth Edition Foes p. 156), 2 Sahuagin Priestess (CR 2: Monster Manual p. 264) [Easy, 1,300 XP rewarded] here. [Customize]

6

This bloodstained room is reinforced by totems across its 20-foot length. A balcony set into the west wall looks upon the room and has three large desks atop it, with a yellow velvet curtain behind them. The thunderous roar of falling water fills this long, low room, and spray makes everything slick and humid. Double doors of stone stand closed to the west.

In this room is a trap. A trigger is hidden within a treasure chest's lock, or in something else that a creature might open. Opening the chest without the proper key causes the stairs to fold in and create a perfectly smooth slide. Creatures on the stairs will fall and slide rapidly to the bottom.

Effect: Targets all creatures on it, steep stairs become a slick slide, causing targets to fall and take 30 (4d10) damage and be knocked prone

Trigger: lock trigger, activates when opened without the proper key.

Countermeasures: A successful DC 20 Intelligence (Investigation) check allows a character to deduce the trap's presence from alterations made to the lock to accommodate the trigger. A successful DC 15 Dexterity check using thieves' tools disarms the trap, removing the trigger from the lock. Unsuccessfully attempting to pick the lock triggers the trap. A web spell or similar can stop creatures from falling down the surface. A set of climbing tools can be used to safely scale the slide. [Customize]

If the room is searched, they find 800 cp, 8000 sp, 1900 gp, 120 pp, Spell scroll (2nd level), Spell scroll (3rd level),

100 gp valuables (900 gp total): Garnet (transparent red, brown-green, or violet), Jade (translucent light green, deep green , or white), 4 Coral (opaque crimson), 2 Chrysoberyl (transparent yellow-green to pale green), and Jet (opaque deep black)

7

The ceiling is almost 80 feet overhead, and bright flecks and glistening granite formations are visible in the distance. A suit of armor, cracked and shiny, stands in a shallow recess. Array windows allow little light to enter this upstairs room. A stone door in the south wall is carved with a dwarf's visage. Frayed blue drapes cover the windows of this circular room, and a heavy curtain hangs across an archway to the north.

In this room is Green Slime (Drops from above. DC 10 Dex, 1d10 acid damage, damage each round until removed. Nonmagical wood, metal weapon or tool used to remove is destroyed. Destroyed by sunlight, cure disease, cold, fire, or radiant)

In the south passage (green) is a large door, locked securely (DC 30) and magically sealed.

8

Resting in a steel stand by the window is a moist bagpipes, and standing quietly in the northwest corner is a tall flute shrouded in moss and leaves. Water gurgles and rushes from somewhere. Destroyed rapiers set around the room suggests a guard might have once been stationed here, while a brilliant forge stand beside the entrance. Double doors of stone stand closed to the east. The north end of this room has collapsed, exposing the room beyond. The tunnel continues on the other side of the room, curving abruptly to the south and out of sight.

In this room is a trap. A pillar of light stretches the location. The trap is activated if the beam is broken by a creature or object and releases spinning blades in the floor or walls. The blades move back and forth along a track, cutting up anything or anyone in their path.

Effect: DC 15 to find, DC 15 to disable
Initiative +2, moves 60 ft. in a straight line each turn. If it enters another creature's space, 17 (4d10) slashing damage. Moves back and forth along a track.

Trigger: light beam, a beam of light activates the trap when broken. [Customize]

In the east passage is an unlocked door.

In the south passage is an unlocked door.

9

The stairs descend into dark, still water that fills an arched room before you. The water's surface is like dark mirrors, disturbed only occasionally by a drop falling from the ceiling. Ten-foot-square cells, their entrances blocked by iron bars, follow both sides of the room. Clinging to the bars of an otherwise empty cell is the decrepit corpse of a male halfling dressed in leather armor. Fountains sit away from the double doors that give access to the room. Double doors of stone stand closed to the west.

In this room is a trap. This trap is activated when a creature touches its surface, which causes the creature to fall through the floor into the hidden pit below. The pits are situated in a row so attempting to jump over the first pit will cause the creature to land in the second.

Effect: Targets all creatures within a 10 ft. square area when stepped on, two hidden pits in a row, jumping over one causes the creature to land on the second. DC 15 DEX save or take 20 (4d10) falling damage

Trigger: touch trigger, activates when surface is touched by a creature.

Countermeasures: A spell or other effect that can sense the presence of magic, such as detect magic, reveals an aura of divination magic around the surface. A successful dispel magic (DC 15) cast on the surface destroys the trap. The pits can be bridged with a plank or sidled via a thin ledge next to the wall. Doing so requires a successful Dexterity (Acrobatics) check. [Customize]

10

Vines fill the staircase, making it difficult to see even the ceiling. Directly across from the window stands a set of double doors in the south wall. Broken couches and a suit of armor are spread on the floor. Two open archways in the west wall lead to another room. The floor past the first archway is damp.

In this room is a trap. This trap activates when a ruby or other valuable item is pried from a statue or other surface, that causes spikes to shoot up through the floor and impale anyone standing above.

Effect: Targets all creatures within a 10 ft. square area, Spikes shoot up through holes in the floor. Any target in the area makes a DC 11 DEX save or takes 10 (2d10) piercing damage.

Trigger: removal trigger, activates when a gem or other valuable item is removed.

Countermeasures: A successful DC 15 Intelligence (Investigation) check allows a character to find a wire attached to the item which triggers the trap when pulled. A successful DC 15 Dexterity check using thieves' tools disables the trip wire harmlessly. A character without thieves' tools can attempt this check with disadvantage using any edged weapon or edged tool. On a failed check, the trap triggers.

[Customize]

In the west passage is an unlocked door.

11

Two simple braziers hang by chains from beams, each casting a bright glow. Benches coated with dust lie about the floor in disordered shambles. On the granite floor, fallen chandeliers lie amid rickety paintings and other furnishings. Two open archways in the north wall lead to another room. The ceiling past the first archway is wet. Long doors of iron-bound oak exit to the south and east.

There is a key here. The key goes into a lock or mechanism, which causes the door to slowly open at the green passage.

In the north passage (green) is a large door, locked securely (DC 30) and magically sealed.

12

From a distance comes the intermittent echo of rough conversational barking. Life-sized busts of dragons line the passageway on both sides, their eyes seeming to follow you. A passage to the north bends out of view, while rotting stone doors obscure a chamber to the west. Next to the exit, battered pots and kettles are stacked all over.

In this room is a trap. +12 to hit against one target, 51 (10d10) piercing damage

Trigger: door, activates when a door or chest is opened.

Countermeasures: The DC to spot the attached wire is 15. A successful DC 10 Dexterity check using thieves' tools breaks the wire attached to the door harmlessly. A character without thieves' tools can attempt this check with disadvantage using any edged weapon or edged tool. On a failed check, the trap triggers.

[Customize]

13

Beneath an unlit lantern hanging from the ceiling, a larger square table is affixed with restraints and stained with old blood. To the east and north are two alcoves strangled with bloodstained cloth and rags. Bits of broken poorly cured animal hides and other debris are sprinkled about the floor. A rough, winding pathway leads toward the south. A constricted corridor leads to another short room after this one. A door stands closed to the east.

In this room is Brown Mold (Frigid temperature. DC 12 Con, 4d10 cold damage, half on save. Immune to fire, causes it to expand. Destroyed by cold)

In the east passage is an unlocked door.

In the north passage is an unlocked door.

In the south passage is an unlocked door.

14

The light from above falls directly on a steel sculpture. A small pot bubbles over volcanic vents in the center of the room, its blue, murky contents churning. A loud waterfall spills down the south wall of this room into the water that fills the room. To the south, huge double doors hang slightly unbarred, and a steady glowing light escapes through the slit. Farther away, a solitary door leads from the west wall.

There are 2 Giant Sea Horse (CR 1/2: Monster Manual p. 328), 3 Kelpie (CR 1: Fifth Edition Foes p. 156), 1 Monstrous Crayfish (CR 2: Fifth Edition Foes p. 70) [Easy, 1,250 XP rewarded] here. [Customize]

In the south passage is an unlocked door.

15

The great arched window along the south wall is dressed by wide black draperies, their golden tassels glinting in the light of two glowing orbs sitting atop lofty tables about the water-filled room. High rims rise 30 feet above the floor on the east, south, and north walls. Bundles of twigs are heaped against the walls. Two doors stand opposite one another in the center of the east wall and the north wall.

There are 4 Tortoise (CR 1/2: Nerzugal's Extended Bestiary p. 21), 1 Hunter Shark (CR 2: Monster Manual p. 330), 1 Fathomer (CR 2: Princes of the Apocalypse p. 207) [Easy, 1,300 XP rewarded] here. [Customize]

In the east passage is an unlocked door.

16

The squat dank limestones of this staircase lead up and down around a 20-foot-wide granite core. Hanging on the north wall is an enamel of a suave, well-dressed woman with a harsh yet piercing gaze. Directly across from the stained glass window stands a set of double doors in the east wall. A lit hallway to the west contains a set of stone doors, through which you hear a low moan.

There are 2 One-Eyed Shiver (CR 3: Princes of the Apocalypse p. 207) [Easy, 1,400 XP rewarded] here. [Customize]

17

The walls of this underwater room are carved with the images of dwarves, and a low natural stone portal stands at the northern end of the room. Mossy and faded mosaics are wrapped by bloodstains. There is a banded door in the west wall and a smaller unbanded door in the east wall. In the middle of the southern wall, a space has been cleared for a simple sleeping pallet and a pair of satchels.

There are 2 Swarm of Quippers (CR 1: Monster Manual p. 338), 1 Crabman (CR 1: Fifth Edition Foes p. 69), 1 Giant Electric Catfish (CR 3: Fifth Edition Foes p. 46) [Easy, 1,300 XP rewarded] here. [Customize]

In the east passage is an unlocked door.

18

This 15-foot-square room is strangled with clutter. Three simple candelabras hang by strings from beams, each casting a luminous glow. The barricade to the north and west are sheathed in steel. A gate of wrought iron stands in the north wall.

There are 2 Green Guardian Gargoyle (CR 1: Fifth Edition Foes p. 115), 1 Deep Scion (CR 3: Volo's Guide to Monsters p. 135) [Easy, 1,100 XP rewarded] here. [Customize]

19

Dirt-caked and ruined frescoes are wrapped by mold. Torn and demolished couches lie in heaps, disordered and spread about. Deep claw marks cover the hardwood furniture, and the once lush upholstery has been sliced to shreds. The door to the north and north are sheathed in steel.

After defeating the Aboleth, the party finds 2600 gp and an Immovable Rod, as well as the gratitude of everyone in Fairlun.

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