The Cistern Lantern

Encounter 2

The final chamber opens into a round well of black water. A lantern the size of a wagon wheel hangs from three chains above it. Its glass is cracked, its flame is green, and the missing brass key turns slowly inside the light as if suspended in deep water.

Setup

The old lantern is both machine and ward. It is not evil, but it is damaged and overcorrecting. Each round, the chamber answers loud violence by releasing more pressure, spray, and echoing bell tones.

Ways to Resolve

Repair: recover the key, calm the pressure valves, and relight the flame.
Combat: defeat or drive off the guardian spirit, then stabilize the lantern afterward.
Bargain: promise renewed maintenance, public remembrance, or a restored river rite.

Skill Challenge: Stabilize the Lantern

CheckCrafting/Engineering to repair, Religion/Arcana to calm the ward, Diplomacy to bargain with the guardian, or Athletics to hold the chains steady while another PC works.

SuccessPC 1 reduces the pressure clock by one step or creates an opening for another PC to recover the brass key safely.

CriticalPC 1 notices the lantern is protecting Greyford badly, not attacking from malice. The party may bargain or repair without finishing the fight first.

FailureThe attempt still reveals useful information, but the water rises, the bell rings, or the guardian gains a better position.

Escalation: if the PCs ignore the lantern and only fight, the water rises each round. At three escalations, the escape route begins flooding and the scene becomes a rescue problem.

Trap

Pressure Sluice

A brass plate in the sluice hall triggers when weight crosses the central channel without first turning the maintenance wheel. The trap is meant to flush debris, not kill intruders, but years of neglect have made it dangerous.

TriggerA creature steps on the central plate or forces the valve door.

EffectA surge of water knocks creatures toward the lower channel and extinguishes exposed flames.

ClueScrape marks on the floor curve around the pressure plate, not across it.

BypassTurn the maintenance wheel, wedge the plate, or open the side drain first.

Skill Challenge: Read the Sluice

CheckPerception to spot the plate, Thievery to wedge it, Crafting/Engineering to understand the valve, or Acrobatics to cross without pressure.

SuccessPC 1 notices the safe path follows old scrape marks along the wall, letting the party bypass or disable the hazard before it fires.

CriticalPC 1 also learns the side drain can be opened to lower water in the final chamber, giving a later advantage at the lantern.

FailureThe trap remains dangerous, but foreshadow it with a groan, shifting water, or a lantern flame guttering before it triggers.

Treasure

Lamplighter's Cache

The cache is hidden behind a loose brick in the valve chamber. It belonged to generations of lamplighters who treated the cistern as a civic shrine.

A polished brass key stamped with Greyford's bridge mark.
A waterproof pouch of coins or level-appropriate currency.
One useful light-themed consumable or magic item appropriate for your system.
A folded maintenance diagram showing the lamp house, bridge channel, and lantern well as one connected machine.

If the PCs report honestly to Lord Greymark and restore the lantern, the city also grants free lodging, ferry passage, or a future civic favor.