Battlemap
Lamprey Cistern
Black water climbs the walls while silver lampreys whisper through the drains.
The Lamprey Cistern is a sprawling sewer complex beneath an old mercantile district, expanded into a prison, shrine network, and hidden slave route by drow engineers. Its lower chambers now serve an aberrant intelligence that breeds in the city's runoff and directs its servants through dreams. The party must navigate flooded passages, concealed doors, and failing sluice machinery before the creature turns the entire sewer into a living nest.
Cold runoff drips from brick vaults, carrying the stink of lamprey slime, wet iron, and spoiled incense. Blue witch-lights flicker in cages above black channels, while distant chains clatter whenever the cistern gates shift. Deeper chambers grow warmer, fouler, and unnaturally quiet.
☠Threat
At the bottom of the cistern dwells the Drain-Mother, an aberrant mass grown from captive brains, sewer parasites, and alchemical runoff. It communicates through dreams and controls the dungeon's leeches, drow handlers, and warped scavengers. If allowed to complete its growth cycle, it will flood the city with psychic larvae that enthrall anyone who drinks from the public wells.
History
The Lamprey Cistern began as a municipal reservoir built over a colony of persistent lampreys that infested the district's old drains. Decades later, the city water office joined its tunnels to a rat catchers guild complex, a merger neither side wanted. Drow slavers seized the expanded works, using the prisons and sluices to move captives. Their experiments awakened an aberration in the lowest settling tank.
Encounter Table
CRA cluster of lamprey-mouthed scavengers wearing scraps of stolen clothing and carrying bits of bone.
Drow slavers in dark cloaks, accompanied by a trained sewer beast and carrying empty manacles.
A pale ooze threaded with silver veins and whispering voices.
A swollen blind crocodile with a lamprey-lined throat and chains embedded in its hide.
Rumours & Whispers
A lamprey the size of a dog was seen swimming through a noble's bathtub before vanishing down the drain.
The drow below do not merely imprison people. They send some captives into the water and listen to what answers.
A hidden shrine can make sewer water run uphill, but anyone who drinks from it dreams of a city made of teeth.
The public wells have begun tasting sweet because something below is learning how to imitate clean water.
Quest Hooks
Quest giver: the exhausted keeper of the public wells
A city's drinking wells have begun whispering the names of missing laborers. The party is hired to trace the contamination to the cistern and recover anyone still alive.
A rare cleansing charm and a civic pardon
Quest giver: a scarred caravan guard
A caravan of prisoners vanished beneath the market district, leaving only broken manacles near a drain grate. Their families want proof of death, but several captives may still be held in room 9.
A rare drow weapon taken from the slavers
Quest giver: a discreet household agent
A noble household seeks a sealed ledger stored in room 22, believing it proves their ancestor funded the sewer's secret expansion.
A rare signet ring that grants advantage on one social check per day
Quest giver: a sleepless plague physician
A fever spreads among creatures that drink from the lower canals. The party must kill the Drain-Mother and return a living sample of its silver leeches for study.
Rare antitoxin sufficient for several doses
Corridor Notes
Thin silver leeches cling to damp stone near every active drain. They recoil from fire but swarm exposed wounds if brushed aside carelessly.
Old sluice markers show competing symbols for a rat catchers guild and a royal water office, both defaced by drow knife cuts.
Black water runs through knee deep channels beneath iron footbridges. Something large occasionally bumps the grates from below.
Thin fungal threads cross the ceiling, twitching whenever the boss in room 21 uses its psychic powers.
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