715 The Flooded Halls of Cerberus – Lv6 Shadowdark Adventure

In the silent depths where ancient forgotten secrets slumber, the whispered echoes of the past ripple across time’s endless currents and tide…

Elvish Adage

In the shadowed depths of the Azure Sea lies a submerged place of ancient and mysterious origin, known as the Flooded Halls of Cerbe­rus. This underwater dungeon, a labyrinth of caverns and dilapidated chambers, has borne witness to the relentless passage of time, its walls worn and smoothed by the ceaseless caress of seawater.

Within, the Flooded Halls unravel like a serpentine maze, a network of caverns and corridors, where the boundaries between natural formation and crafted archi­tecture blur. The walls of these chambers are encrust­ed with barnacles and coral, and luminescent algae cast an eerie, undulating glow, revealing faded murals and in­scriptions of a lost civilization. These scenes depict a so­ciety that once harmonized with the sea, worshiping dei­ties of the deep and mastering forgotten aquatic magics.

Spectral Sentinels

The Echoing Vaults hold the remains of those who served this temple. They are lined with stone sarcoph­agi, each bearing the effigy of its occupant. The guard­ians of this sacred necropolis are the Spectral Sentinels, ethereal apparitions that drift through the water, their eyes aglow with a ghostly light, eternally vigilant.

The dangers within the Flooded Halls of Cerberus are as numerous as its mysteries. From the treacherous cur­rents that swirl through its passageways to the ancient traps and arcane wards still active after centuries. But it is said that hidden within its confines are treasures and secrets of the old sea magic, waiting to be rediscovered by those daring enough to plunge into its depths.

Adventure Hooks

  • Dark Rituals. In the bustling tavern of Port Marrow, a grizzled sea captain shares whispers of the Flooded Halls of Cerberus, an ancient, sunken temple where treasures of a lost civilization lie hidden beneath the waves. A mysterious, sea-weathered scroll, half-eaten by time and salt, speaks of a powerful artifact, the Heart of Tides, capable of controlling the very seas, said to be enshrined within its deepest chamber. A local sage named Otto Platter offers a substantial reward for any relics or knowledge recovered from this crypt. Howev­er, a foreboding warning accompanies these tales – eerie disappearances of sailors near the site suggest that the temple’s guardians may still lurk in the shadowy depths, protecting their sunken secrets. (600 gp, 5 XP).

Level 6 Adventure

  • Danger. Risky. Check for a Random Event every 3 crawling rounds and after loud noises (4-in-6 chance).
  • Luminous Bio-luminescence. Throughout the dun­geon, bio-luminescent organisms cast a haunting yet beautiful glow. This natural light source varies from the soft, eerie luminescence of algae on the walls to vibrant, colorful displays from schools of luminescent fish and jellyfish. These living lights create an otherworldly aura, illuminating ancient frescoes and forgotten inscriptions, and guiding visitors through the submerged corridors.
  • Wards and Traps. These range from glyphs that trig­ger tidal surges in narrow passages to more complex spells that summon guardians. All traps described below reset after 2 hours after being triggered.
1 A sudden underwater tremor dislodges an ancient statue, revealing a hidden compartment with a pearl (300 gp, 3 XP).
2 The ghost of a drowned priestess appears. She means no harm and if the characters do not react aggressively, the specter offers cryptic guidance before vanishing into the watery shadows. This means two random characters earn a luck token.
3 An ancient mechanism is accidentally triggered, causing the water in area 10 to filter out and remain at waist level for 1 day.
4 A swarm of electric eels, disturbed from their slumber, forms a living barrier in a narrow corridor. The characters can attack them to scare them away (HP 26, AC 11). Otherwise, they take 1d6 damage if they swim through the eel school.
5 The characters disturb a solitary shark. The beast fights until slain if one of the intruders bleeds, otherwise, it flees at half HP.
6 The Heart of Tides (area 4) pulses, causing the water to shift. The heroes are transported to another area (GM’s choice).

An Underwater Quest

Consider the following: Adventurers must equip themselves with magical means to breathe underwater, visibility is reduced, and heroes must devise alternative ways to communicate effectively underwater, as normal speech is impossible. Additionally, movement through water is slower and more cumbersome than on land. Heroes must deal with buoyancy and resistance (slashing or bludgeoning attacks are made with disadvantage).

1. The Shore

The heroes follow Otto Platter’s instructions and walk the length of the shore until they find a grotto with a mys­terious pool within. Unfortunately, they are not the only ones looking for the Heart of Tides or ancient treasure. Six pirates and their leader (orc chieftain) arrive at the same time. They are not sure about sharing the sub­merged treasure within the dungeon (Reaction).

If Life Gives You Lemons. The pirates carry a box with several Amulets of the Depths. They are delicate, aquamarine pendants, encased in a spiraling shell of sil­ver. When worn, it envelops the bearer in a thin, shim­mering bubble of air, granting the miraculous ability to breathe freely while submerged in the deepest of waters. The characters can use the amulets if they work together with the pirates or if they get rid of them.

2. Wet Descent

The dungeon’s entrance is nestled among the rugged cliffs that flank the windswept beach. This shadowed grotto, half-hidden by cascading sea vines and weath­ered by the salt and spray of the ocean, whispers of un­told secrets and tales from bygone eras.

3. Cavern

A swarm of piranhas inhabits this cavern. The carni­vore fish recklessly attack and fight until slain if any in­truder bleeds. Otherwise, they flee at half their HP.

4. The Heart of Tides

Suspended in the water like a celestial body floats the Heart of Tides. This enigmatic orb, pulsating with a deep blue luminescence, is encircled by sinuous tendrils that emanate from the surrounding walls, resembling the arms of a giant octopus.

These living tendrils, covered in suckers and shimmer­ing with a bio-luminescent sheen, undulate gently, cre­ating an eerie dance. They react with swift, coordinated strikes to ward off any who dare approach.

  • Tendrils. Eight arms protect the Heart of Tides (HP 8, AC 12 each). They sense all living creatures within 15 feet and can attack anyone within that range. Slam + 3 (1d6). A target hit by two or more tendrils is grappled and restrained (DC 14 STR to break free).
  • Treasure (6 XP). The Heart of Tides has the incred­ible power to control any body of water in a specific way once a week. The user ages 10 years after each use.

5. Nautilus Engines

Colossal nautilus shells, ancient and encrusted with lay­ers of coral and barnacles, are strategically positioned. They work as the dungeon’s living engines, rhythmical­ly expelling jets of water, maintaining a constant flow through the labyrinthine passages. The harmonious co­ordination of these nautilus engines is a marvel of both natural design and ancient engineering, integral to the life and breath of the dungeon’s mysterious ecosystem.

  • Deactivation. The characters can use a dispel mag­ic spell to cause the five engines in here to stop working. This causes the water level to drop to chest level. Four zombie sahuagin emerge from a hole in the wall.

6. South Cavern

A swarm of piranhas inhabits this cavern. The carni­vore fish recklessly attack and fight until slain if any in­truder is bleeding. Otherwise, they flee at half their HP.

7. Antechamber

This area is half-hidden behind a curtain of luminescent kelp. Within this grotto rest two chests, their wood swol­len with moisture and banded with rusting iron.

  • Treasure (2 XP). There are hundreds of silver coins from a forgotten era (300 gp), a +1 dagger, and three small vials filled with red fluid (potions of healing).

8. Central Cavern

A vast cavern opens up, its walls scarred by the passage of time and the marks of countless battles. Here prowls an adult, scarred shark, the undisputed ruler of this un­derwater domain. The large marine carnivore fights un­til slain if any of the characters bleed. Otherwise, the shark attempts to flee when reduced to half its HP.

9. Secondary Engines

  • Deactivation. A dispel magic spell shuts down these engines. This causes the water level to drop to chest lev­el (waist level if the engines in area 5 were deactivated). Four zombie sahuagin come out from a hole in the wall.
10. The Halls of Cerberus

The Hall of Cerberus stands as a grand testament to the lost artistry of its creators, the central statue features three heads snarling menacingly toward different paths. Intricate mosaics depicting scenes of popular myths and legends adorn the eroded walls.

A three-headed beast made of dark water is Cerberus’s manifestation (greater water elemental). Three zombie sahuagin come to its aid. Once defeated, the characters can freely explore the area and retrieve the treasure.

11. Secret Vault

A slithering dark tunnel stands between the characters and their well-earned loot. There are four stone chests.

  • Treasure (6 XP). A great hoard is found. There are 3,540 gp and 2,893 sp in leather bags. There is a pearl (40 gp), a suit of dwarf-made chainmail (60 gp), an ivo­ry tusk carved with angels fighting demons (80 gp), and stored in a beautiful container, a Kytherian Cog.

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