Zone 3: The Sump

Updated: 2026-02-26

Deep Underhive

The Sump is where the underhive ends and something older begins. Near-lawless, lightless, and barely mapped, this is the domain of mutant warrens, ancient vaults, and things that should not be disturbed. Only the most powerful gangs venture here - and not all return.

Character

The Sump exists in permanent darkness. Pitch Black rules apply to every territory here - lumen-strips don’t function this deep, and even the most powerful lamp packs illuminate only a few metres before the dark swallows the light. The architecture changes as you descend: hive-standard construction gives way to older structures, pre-dating the hive itself. Walls of fused rock. Archways carved with symbols no one recognises. Machinery built to a scale and purpose that defies understanding.

The temperature drops. The air is thick with particulates that make rebreathers clog and misfire. Water doesn’t pool here - it seeps, rising from somewhere below in a slow, relentless tide that coats everything in a thin film of oily residue. The ground is treacherous: metal grating over black water, unstable rubble, sinkholes that open without warning.

And there are sounds. Not the mechanical clatter of the District’s pumps or the human noise of the Sprawl. Down here, the sounds are organic. Scraping. Clicking. Things moving in the water. Occasionally, a low vibration that might be machinery - or might be something breathing.

Key Locations

The Bone Reach - A long, low tunnel whose walls are embedded with fossilised remains - human and otherwise - fused into the rock over millennia. It’s the primary route into the deepest Sump territories. Gangs paint kill-marks on the bones as they pass. Not everyone who enters leaves a mark.

The Blind Eye - A vast, circular chamber with a domed ceiling lost in darkness above. An ancient oculus at its centre stares upward at nothing. The acoustics are disorienting - whispers carry from one side to the other while shouts seem to die within arm’s reach. It’s the closest thing the Sump has to a landmark.

Vault Primus-IX - Sealed since before the founding of the hive, or so the reclaimators claim. Its door bears the marks of a dozen failed breaching attempts. Whatever is inside is protected by mechanisms that still function after millennia. The Arc III climax scenario centres on reaching this vault.

The Seep - The lowest accessible point of Sump Sink-17. A cavern where the floor is entirely submerged in black, warm liquid that no cogitator can fully analyse. Things live in the Seep. Occasionally, things come out of the Seep. Fighters stationed nearby report nightmares and nosebleeds.

Atmosphere & Narrative Notes

The Sump is the campaign’s endgame territory - the place where dominant gangs stake their claim to the richest and most dangerous ground. The x2 income modifier and Pitch Black rules make every battle here a high-stakes affair. The one-territory cap means gangs must choose their Sump territory carefully; there are no second chances.

The Sump is not just dangerous in the way the Sprawl or District are dangerous. It is wrong. The architecture doesn’t make sense. The creatures down here aren’t underhive fauna - they’re something else. And the deeper the gangs dig, the more the Sump seems to respond. Not with intelligence, exactly. With hunger.

The Sump starts the campaign at Contamination 1 - the only zone that begins with active contamination effects. From the very first battle fought here, fighters not in cover risk Flesh Wounds from the Bad Air. By Arc II, the ground itself becomes treacherous. By Arc III, the fog rolls in. By the campaign’s later arcs, the Sump reaches Contamination 5 - the maximum - where fighters taken Out of Action are dragged into the dark and must be rescued or written off. But the contamination does not stay at its peak forever. The Deepening is a tidal cycle: once all zones reach maximum contamination and the Sealing the Seep scenario is played, the tide turns and contamination begins to fall. The Sump never drops below Contamination 1 - it is always dangerous - but the worst effects recede until the cycle begins again. See The Deepening for full contamination mechanics.