The Lighthouse at the Bottom of the Sea

Game system: dnd5e

Relight a drowned beacon before the trench-things wake -- and decide the fate of a keeper who bargained with the dark.

PREMISE The Saltveil Deep currents have shifted. Three merchant ships have run aground on the Sheercut Reefs in a single week, and a fourth is missing. The old lighthouse at Gravemark Point was supposed to guide ships clear -- but three months ago, a storm surge swallowed it whole, keeper and all. Sailors report seeing a light flicker from the submerged tower at night, then vanish. The harbor council is offering 300 gp to anyone who can reach the lighthouse, determine why it failed, and relight the beacon by dawn -- before the trench-things that the light kept at bay remember how to come close to shore. BACKGROUND (GM ONLY) The lighthouse keeper, Osmer Pale, did not drown. He became something else. The trench-things -- deep-dwelling creatures of pressure and darkness called the Unlit -- had been kept away from the shallows by the lighthouse for eighty years. When the storm took the lighthouse, the Unlit began circling. Pale made a bargain: let them feed on his memories in exchange for the ability to survive in the deep. Now he has forgotten almost everything about himself, but he remembers the lighthouse. He tends it still, turning the great lens by hand in the dark. The problem: the oil reservoir is dry. Without fuel, the lens cannot ignite. And the Unlit are growing bolder by the night. HOOKS 1. The party is hired directly by the harbor council: 300 gp, diving gear provided, eight hours to complete the task. 2. A sailor paces the docks, his vessel moored and unable to leave -- his crew is aboard that fourth missing ship, last seen near the Sheercut Reefs. He will pay the party expenses to go. 3. One party member receives a soggy note slipped under their door, written in careful faded ink: "The light can be saved. The keeper is still there. Do not be afraid of what he looks like now." 4. A Depths-Sworn initiate approaches the party with a counter-offer: reach the lighthouse and sabotage the oil reservoir instead. The fee offered is generous. The initiate does not explain why. ACT 1 -- DESCENT AND PRESSURE Read aloud: The water is colder than it should be for the season. Thirty feet down, the light from the surface becomes a memory. The lighthouse tower rises from the seafloor ahead, encrusted with barnacles, the iron door still standing. Something moves at the edge of your vision, just beyond the range of your lantern -- too large to be a fish, moving with a patience that feels deliberate. The party must descend with thirty minutes of water-breathing remaining (track this as a hard cap). The Unlit are present but not yet hostile: treat them as ambient dread. A DC 12 Perception check reveals they move in patterns -- circling, never approaching within twenty feet of the lighthouse walls. Skill check: DC 14 Strength (Athletics) to force the iron door open against pressure and rust, or DC 13 with thieves tools to work the corroded lock mechanism. ACT 2 -- THE KEEPER Read aloud: Inside, the lighthouse is impossibly intact. A spiral stair leads up. Cold light filters from above. Halfway up the stair, a figure sits -- soaking wet, wrapped in a keeper coat, staring at a small timepiece that has not worked in months. He looks up. His eyes are entirely dark. Osmer Pale is not hostile. He is fractured. He knows the lighthouse needs fuel, but he cannot remember the word for fuel. He calls it "the burning thing that feeds the turning." He knows where a cache is stored -- below the waterline in a sealed sub-cellar -- but the Unlit have gathered there. He cannot go near them; per the terms of his bargain, he must remain in the lighthouse. Skill check: DC 13 Insight to understand that Pale is telling the truth about his limitations. DC 14 Persuasion to convince him to draw a map of the sub-cellar in the condensation on the lens glass. ACT 3 -- THE SUB-CELLAR Read aloud: The sub-cellar is below the lighthouse base, accessed through a hatch in the floor. The water here is perfectly still. Three oil canisters rest in a rack on the far wall. Between you and them, four shapes drift in the dark -- vaguely human in outline, trailing wisps of shadow, utterly silent. The Unlit are not part of the bargain. They must be bypassed or driven off. They are repelled by direct light -- torches, lanterns, light cantrips -- and any such source in their space forces them to retreat that round. The party can use this to herd them away from the canisters without fighting. Each oil canister weighs 30 lbs; the party needs at least two to fill the reservoir. Skill check: DC 12 Stealth to move past a drifting Unlit without drawing its attention. DC 13 Athletics per canister to carry it up the hatch quickly. SECONDARY LOCATION: THE WRECK-STACK Half a mile from Gravemark Point, five wrecked vessels have piled against a submerged shelf over the past decade, forming a compressed tower of timber, cargo, and corroded iron. The Wreck-Stack sits in forty feet of water and is visible from the surface at low tide. It is not required for the main mission, but it contains: - The fourth missing ship (the Cassock-Tine), wedged into the middle of the stack, with its crew barricaded below decks and surviving on bilge water and ship biscuits. - A driftwood marker scratched with the Depths-Sworn sigil, indicating this site is theirs. - In the lowest wreck, a waterproof lock-chest containing three vials of deep-oil (each worth 50 gp and usable as fuel for the lighthouse, making an alternative to the sub-cellar). Including the Wreck-Stack: The crew rescue adds a time-pressure branch. If the party splits, they face parallel deadlines. Reward the crew-rescue branch with a bonus 100 gp from the sailor on the docks (Hook 2) and one dose of briny-blessed seawater (advantage on Charisma checks with denizens of the deep for 24 hours). SECONDARY LOCATION: THE BRINE ANCHOR TAVERN The Brine Anchor is a two-story waterfront tavern that smells of brine and rancid tallow. Its owner, a wide woman named Grette Mull, is not a Depths-Sworn member but rents the back room to Sister Callowmere's group for a generous monthly fee and asks no questions. The back room contains a locked cabinet with Depths-Sworn literature (recognizable as heretical by DC 12 Religion check), three hammocks strung between iron hooks, and a corkboard covered in tide charts with red-inked circles marking deep-ocean grid coordinates. Grette will lie for the cultists if pressed but she is a poor liar (DC 11 Insight to catch it). She will give up the back room's tenants immediately if threatened with involvement in a council investigation. The corkboard tide charts, if studied (DC 14 Investigation), reveal the Depths-Sworn believe a specific low-tide window two nights from now will allow the Unlit to cross into shallower water permanently -- which is why Sister Callowmere is so urgent about sabotaging the lighthouse before then. KEY NPCS Osmer Pale, the Keeper. Motivation: become human again, or failing that, ensure the light keeps burning. Quirk: speaks in fragments, substituting descriptive phrases for nouns he cannot recall -- "the hot ball that moves across the up-space" for the sun, "the long wet dark" for the ocean. Councilor Brenn. Motivation: protect Saltveil shipping lane revenue. Quirk: refuses to admit the Unlit are real, insisting they are "unusual deep fauna" and not something to negotiate with. Maret, a stranded sailor. Motivation: locate the missing fourth ship. Quirk: keeps a list of the missing crew names in her coat and counts them like a mantra when she is frightened. Sister Callowmere, Depths-Sworn Initiate. Motivation: hasten the Unlit arrival in the shallows -- the cult believes the Unlit are gods returning to a world that forgot them. Quirk: speaks of the Unlit with reverent calm, will not lie directly but will omit crucial information. She can be reasoned with if the party proves the Unlit are indifferent to their worship -- DC 16 Persuasion, advantage if the party has witnessed the Unlit ignoring a Depths-Sworn symbol. Tethram Vos, Salvage Diver. An elderly man who has worked the Sheercut Reefs for forty years. He knows every wreck and every current and will not enter the water anymore -- he stopped three years ago, when something followed him up from a dive. He has not explained what. He is the best source of tactical information for the mission: he can describe the lighthouse exterior, the sub-cellar hatch location, and the rough behavior of the Unlit (he calls them "the Drift"). He charges 15 gp for a full briefing and lives on a converted lugger moored to Dock 9. Motivation: he wants to know what followed him up from that dive, but does not want to be anywhere near it again. FACTIONS THE HARBOR COUNCIL: Practical, mercantile, afraid. Wants the lighthouse relit, wants no awkward questions about what the Unlit are. Will pay promptly and pretend nothing unusual happened. THE DEPTHS-SWORN: A small cult -- a dozen members in Saltveil at most -- who believe the Unlit are ancient divine beings suppressed by civilization's light. They are not violent by default, but they will interfere with the mission through misdirection, bribery, and blocking access to diving equipment rental. Their window is the low-tide two nights from now; if the party delays past that, the Depths-Sworn escalate to direct interference. They operate out of the back room of the Brine Anchor tavern. THE PALE-WATCHERS: An informal network of three Saltveil sailors and one retired harbormaster who have been quietly documenting the Unlit's movements for two years. They believe the Unlit are not divine -- merely hungry and patient -- and that the lighthouse is the only thing keeping the shallows safe. They have a crude but accurate map of Unlit patrol routes in the waters around Gravemark Point. They will share it freely if the party can demonstrate they intend to relight the beacon. Their leader is Duvaine, the retired harbormaster, who runs a chandlery on Dock Row and smells perpetually of whale oil. They are not fighters and will not go into the water. EQUIPMENT AND PREPARATIONS The harbor council provides diving gear to hired parties: two sets of sealed water-breathing apparatus (30 min each), waterproof lanterns (1 hour burn time), a rope harness, and one grappling hook. Additional supplies available for purchase on the docks: hemp rope (1 sp per 5 ft), sealed oil canisters (2 gp each, usable as backup lighthouse fuel), underwater signal flares (5 gp each, repel Unlit for one round when triggered). If the party gathers intelligence before diving: speak with dockworkers (DC 11 Persuasion, learn the storm pattern that took the lighthouse); consult tide charts at the harbormaster office (DC 13 Investigation, learn that Unlit sightings follow the lunar low-tide); check the lighthouse registration with the maritime guild (DC 10 Investigation, learn that Osmer Pale filed a replacement-oil requisition three days before the storm -- the oil was never delivered and sits in a guild warehouse, available for 8 gp per canister if the party produces a council writ). THE TWIST Pale's timepiece is not broken. It is counting down. His bargain with the Unlit expires at dawn -- at that moment he will become fully one of them. He has been tending the lighthouse desperately, hoping the light will sever the connection before the bargain completes. He has not told the party this because he cannot remember the words for time or morning. CLIMAX At dawn (when the session timer runs out or the party delays too long), the Unlit surge. Four Shadows (CR 1/2, HP 16, AC 12, Strength drain on hit: DC 13 Constitution save or -1d4 Strength) converge on the lighthouse. Pale begins to change -- he can hold the stair for two rounds with DC 13 Strength checks before losing himself entirely. The party must get the oil into the reservoir (one action per canister, DC 11 Athletics) and trigger the ignition (DC 14 Arcana or tinker tools check). When the beacon fires, all Shadows flee the light. Pale -- if the light catches his eyes at the exact moment of ignition -- is pulled back from the bargain. A DC 14 Wisdom saving throw determines whether he holds on. The dice make the ending. RESOLUTION AND REWARDS Success: 300 gp from the council, plus Pale's timepiece (advantage on Initiative while underwater, as long as you wind it each morning). The fourth ship is found drifting but intact; its crew spent three days below decks in silence. Pale, if saved, becomes a recurring contact with fragmentary but genuine knowledge of the deep. Duvaine and the Pale-Watchers become long-term allies -- they have been watching for two years and have much to share. If Pale is lost: The beacon lights. The Unlit retreat. Somewhere in the trench, a new one drifts -- and carries the faint memory of a timepiece ticking. RUNNING IT Track time visibly. Write "30 min" on a piece of paper at the start and cross minutes off whenever the players pause, debate, or backtrack. The pressure is both a mechanic and an atmosphere. Pale's fractured speech is a puzzle as much as a roleplay encounter. Reward players who take notes on his phrasing and translate it back to him -- he responds with more coherent answers when addressed in his own terms. Scaling up: Increase Shadows to six; require three successful DC checks for ignition rather than one. Add a Depths-Sworn ambush at the surface when the party resurfaces. The Pale-Watchers' route map is stolen before the party can retrieve it. Scaling down: Give the party 45 minutes of air; lower the Athletics and Arcana checks by 2 throughout. The Pale-Watchers approach the party unprompted with the route map as a gift. --- **SETTING** Vel Soth was a tidal city built on a submerged ridge, two hundred feet beneath the Saltveil. Its streets are intact; its inhabitants are not. A ring of pressurised dive-bells operated by competing guilds encircles the ruins, each claiming a sector. **FACTIONS** *The Brackwater Guild* — Pragmatic salvagers controlling the only functioning dive-bell in the central district. They hire outsiders for work too dangerous or too conspicuous for their own members. Loyalty is for sale at a fair price. *The Tidewarden Remnant* — Survivors of a monastic order devoted to a sea deity whose name erodes from stone faster than tides should allow. They believe Vel Soth is a lock, not a ruin, and that someone is looking for the key. *The Abyssal Compact* — A confederation of pressure-adapted creatures treating the deep shelf as sovereign territory. They tolerate surface divers who observe their depth markers; they do not forgive those who don't. **KEY LOCATIONS** *The Spillway Bazaar* — A floating market at the old harbour mouth. Every guild keeps a stall here; information is the most valuable commodity. *The Velvet Dark* — Below 200 feet, light spells require concentration checks and sounds carry in impossible directions. Vel Soth's inner sanctum rests here. **HOOKS** 1. A Brackwater diver surfaced babbling a set of coordinates before losing consciousness. The coordinates fall inside Compact territory. 2. The Remnant offers a substantial reward for the return of a relic described only as "the thing that hums when held near salt." 3. A Guild contract gone wrong left a team trapped in a sealed antechamber. Air is finite. Someone has to go back in.

Tags: ["survival", "horror", "saltveil", "underwater", "mystery", "factions", "intrigue", "exploration"]

A community tabletop RPG campaign shared on TableTop DLC.