In this short adventure, a school of kuo-toa fanatics attacked a small fishing settlement in search of suitable sacrifices to their deity. This is a low-stake, low-tier adventure that you can include as a sidequest in any small to middle-sized settlement. The encounters and treasure below are balanced for a party of 4-6 level 3 characters.
A school of kuo-toa fanatics has risen from the depths of the ocean. They follow a self-appointed priest who has led them for at least a year. Their priest, Blin-dul-boog, informed them a few months ago that it has felt the strong influence of an obscure deity of old named Dagon. To them, Dagon is a powerful entity that shall bring them gifts and influence in the world. The otherworldly perceptions of the kuo-toa attuned to Blin-dul-boog’s and the whole group became focused on finding the ancient place of worship that the priest mentioned. After months of searching, the kuo-toa found an arcane, semi-submerged, forgotten temple to Dagon. The place is in shambles but the main sanctum is in good enough condition. The four limestone statues of the fish, god-like entity were proof to the fish folk that this was the right place.
The kuo-toa are prone to worshipping obscure entities from beyond the Material Plane without much knowledge or practical experience with them. Their form of worship is evolving and almost improvisational. Priest Blin-dul-boog spends long hours among the limestone statues communing with Dagon. It has become the voice of their impromptu religion and everything he says is considered sacred scripture to the other kuo-toa. Blin-dul-boog has instructed the others that, in order to gain Dagon’s favor, they must bring human sacrifices and burn the bodies in the magical circle in the sanctum. Only then, will Dagon look their way and pamper them with its gifts. The other kuo-toa saw no incongruence with the plan and went out to find humans for sacrifice. The fish folk are not numerous enough to raid a settlement so they have chosen to follow and attack small fishing parties. Over the course of several weeks, they have had mixed results. Sometimes the fishermen manage to scare them off, other times the kuo-toa manage to extract a person and bring the victim to the sanctum.
The fishermen live in the small town of Amira. The townsfolk panic because the fishermen are unwilling to risk their lives any longer until the problem is solved. However, waiting too long could cause the local economy to collapse and many people to starve. Townspeaker Challa has vowed to put a stop to the hostilities at sea. He has posted an attractive bounty contract to incentivize traveling mercenaries and sellswords to take care of the problem without risking any more local lives.
The kuo-toa have attacked fishing boats over the past three weeks. Four fishermen have gone missing and are presumed dead. The de-facto leader in the fishing settlement of Amira, Townspeaker Challa, offers a considerable bounty to passing mercenaries and adventurers. He wants the scary fish folk dead. He offers 300 gp for the elimination of the fish creatures.
In addition, retrieving the bodily remains of the four missing fishermen is worth an extra 40 gp. He explains that this is almost impossible since the ocean is so vast. It would only be possible if the kuo-toa brought the poor fishermen back to their lair.
Townspeaker Challa reveals that the kuo-toa have been seen frequently near a small rocky island formation. Sailors avoid it because the exposed rocks can cause serious structural damage to most ships. A brave local sailor is willing to bring the adventurers to the place in his fishing boat. He too is getting a moderate reward for this service.
Circling around the rock formation and following the occasional trail of kuo-toa swimming, the sailor brings the characters to a covered cove that leads to area 1. It is an underground submerged cavern with a large double stone door and six pillars.
The following descriptions of areas 1 through 11 correspond to Dagon’s Sanctum map.
Terrain. The limestone flooring of the sanctum is in terrible condition. Some parts are broken, others have degraded into fine sand. The water erosion and salinity in the tiles reveal that the entirety of the dungeon becomes submerged for extended periods of time. Perhaps the temple is only so exposed during this season.
Doors and Obstructions. The two double stone doors stand on old but still serviceable rails. A creature can move any door to the side by spending an action. Some of the hallways in the dungeon have collapsed completely. The packed rubble prevents any movement. Besides, clearing any of the blockades is an impossible task that may well cause more structural damage to the structure.
Submerged Tunnels. A network of natural submerged tunnels connects several areas of the dungeon (see dotted lines in the illustration). The tunnels are short enough that any creature can swim through them in single file, assuming the bring a light source with them. Fighting the kuo-toa underwater is a terrible choice because they are not penalized with disadvantage for it. In addition, the fish folk can breathe underwater.
Light. All of the areas in Dagon’s Sanctum are in complete darkness except for the main sanctum (area 10). Four magical torches on sconces with continual flame spells provide bright light.
Smells and Sounds. The smell of brine and rotting algae are prevalent throughout the structure. The distant sound of shallow crashing waves from area 1 fades as one explores the place further.
Six pillars flank a narrow passage to a set of large stone double doors. The doors used to be engraved with delicate and complex bas-reliefs but little remains of them. The water erosion and colonization of corals and barnacles have rendered any chance of legibility impossible in both sides of the door. A human femur bone lays scattered on the floor in front of the entrance.
Submerged Tunnel. The characters can use an underwater tunnel to the east of the entrance to swim to area 3 and area 4.
2. Broken Hallway
The walls and ceiling of the hallway collapsed ages ago and closed of this passage. Clearing it or digging through it is, in practice, impossible. A kuo-toa whip looks around the surface rubble in search of valuables trinkets. It looks up in surprise and gets ready to fight the invaders.
3. Small Nest
There are three kuo-toa and one kuo-toa whip in the room, tending to the eggs in the nest. They are very territorial and defend the nest fiercely. One of the kuo-toa doesn’t join the fight and attempts to grab as many eggs as possible and jumps into the pond. It tries to bring them to area 7 for safeguarding.
Submerged Tunnel. The characters can use an underwater tunnel in the pond to swim to area 4.
4. Meditation Room
There are a limestone tabernacle of sorts next to the north wall and two stone incense burners. They are all eroded beyond recognition. A mural on the wall has peeled off enough that nothing of it is distinguishable anymore. There are two kuo-toa whips hidden in the pond, ready to pounce when an adventurer gets close enough to the water.
If the adventurers come this way through the submerged tunnel, the two kuo-toa fight them underwater and try to foil any attempts at leaving the water.
Submerged Tunnel. The characters can use an underwater tunnel in the pond to swim to any of the other areas connecter to it. This location is directly connected to all others.
5. Altar of Tentacles
This location can only be reached from the underwater tunnels. An ineffable altar attached to the north wall of the room defies all explanation. Two dozen octopi and squid tentacles are attached to a limestone slab on the wall. The tentacle trunks are fused to the stone and appear to be a part of it. The tentacles are alive; they wiggle and move around as if trying to grasp something. If a non-kuo-toa creature approaches within 5 feet of the altar, it must make a successful DC 14 Strength saving throw to avoid becoming grappled. Once grappled, the creature takes 7 (2d6) bludgeoning damage in any subsequent turn as the tentacles attempt to constrict the creature. The altar can grab up to two medium-sized creatures at the same time.
There are two kuo-toa and two kuo-toa whips in the room tending to the nest. They fight fiercely. If any of the kuo-toa whips manages to use its Pincer Staff ability, they attempt to push their targets to the tentacles on the wall.
Submerged Tunnel. The characters can use an underwater tunnel in the pond to swim to area 4 or area 7.
Secret Door. A hidden button next to the altar of tentacles causes a section of the wall to slide outward and reveal a secret passage to area 9. A creature can find the button with a successful DC 14 Intelligence (Investigation) check.
6. The Great Door
The northmost section of the main hallway continues after the debris pile in the middle. It ends with a double set of stone doors similar to the ones in area 1. The state of conservation of these limestone doors is marginally better than the ones in the entrance. The bas-relief on the door, while eroded and cracked, is somewhat legible. It depicts a grand semi-humanoid, toad-like, reptilian creature with large fangs and several tentacles. The creature emerges from the ocean and howls at the sky. A successful DC 17 Wisdom (Religion) check reveals this is an Old One named Dagon. It is an obscure entity that is said to roam the deep oceans. The true king of the depths.
The doors are closed but unlocked. Opening this door triggers the ambush encounter in area 10
7. Large Nest
The group of kuo-toa in this room appears to be in a frantic panic. Some of them gather as many eggs as possible in algae baskets to move them away to the cavern complex in area 8. Their intention is to keep as many eggs as possible safe from the intruders. The rest of the fish folk stand guard and protect the ones tending to the nests. Two kuo-toa whips and three kuo-toa fight to the death.
Submerged Tunnel. The characters can use an underwater tunnel in the pond to swim to area 5 and area 4.
8. Cavern Access
A cave-in during an earthquake a couple of decades ago opened this passage. The tunnel leads down to a gigantic network of tunnels and semi-submerged chambers. The network eventually connects to the Underdark in several locations under the seafloor level. The kuo-toa have only partially explored some caverns that allow them to escape back to the ocean waters. The contents and perils of these caverns are not within the scope of this module and are left to the DMs discretion.
Secret Door. A section of the wall adjacent to area 10 is fragile and cracked. The light from the magical torch in the sanctum filters through the cracks and is visible if no other light source is available. A creature can dig through the rubble and break down the wall with a successful DC 16 Strength (Athletics) check.
9. Secret Passage
This empty side room remains unknown to the kuo-toa. There is nothing of value in the room. The two secret doors to area 5 and area 10 are not hidden from this side. The outlines of the doors are visible and each of them has a handle to pull them inward. If the adventurers use the secret door to area 10, they avoid the ambush attack and may surprise the kuo-toa in the room.
10. Dagon’s sanctum
Blin-dul-boog (kuo-toa archpriest) stands in the center of the room by the magic circle. The mistreated remains of the missing fishermen lay at its feet. The priest must interrupt his dark ritual to confront the intruding adventurers.
There are four kuo-toa close to the south door ready to use their Net ability to restrain the adventurers. The two kuo-toa whips use their sacred flame spells as soon as the doors open. Afterward, they use their Pincer Staff attack to prevent the adventurers from reaching the priest. The archpriest uses his spirit guardians spell as soon as the encounter begins.
Secret Doors. Pulling the southeast sconce causes a section of the wall to slide outward and reveal a secret passage to area 9. Pulling the northeast sconce produces the same effect to reveal a secret passage to area 11.
The kuo-toa have hidden things of value in this room. Some of them were recovered from the bottom of the ocean, others were stolen from fishermen and merchants. The two wooden chests contain an ancient belt with a bronze buckle (60gp), a sturdy limestone tiara, inlaid with oak wood (60gp), a rough wool hat (30gp), an old alabaster jewelry box (80gp), a durable dragonbone amulet with a black pearl (500gp), a sturdy silver tiara, set with a carnelian (95gp), an engraved soapstone cup, set with a malachite (70gp), an engraved carved wood figurine of a ship, set with an obsidian piece (70gp), and 450 gp.