Warren of the Gnawing Dark
The corridor stops being a corridor. The walls go soft — matted, fibrous, layered a foot thick with chewed cloth and hair and bone-meal — and the ceiling drops to shoulder height and then to less. The whole surface is moving slightly, the way a field moves.
There is no squeaking. That is the wrong thing about it. Thousands of somethings are working in the dark on every side of you and the only sound is a dry, continuous, patient gnawing.
DM summary. A rat-warren with a disease-spirit in the middle of it, in tunnels too low to fight properly. Fire clears the room and fire is also the party's air supply, and the honest solution is to burn the nest-mat and get out fast.
Terrain & Features
Battle map: The Wormways — pages 17 & 18, 110 × 75 ft
The wormways ARE the warren: 100 × 60 ft of branching tunnel, printed. Mark the three squeeze tunnels at 4 ft high, shade the nest-mat chamber, and chalk the draught arrow along the north tunnel.
- Dimensions. 100 ft × 60 ft overall, and a branching warren rather than a chamber: three tunnels, each 30–40 ft long and 4 ft high (Medium creatures squeeze — half speed, disadvantage on attacks, attacks against them have advantage), meeting in a 20 ft × 20 ft chamber with a 7-ft ceiling. Draw it as a Y on the mat; almost all of that box is empty rock.
- Light. None, and it eats light: the matted walls give no reflection at all, so a torch lights 15 ft here instead of 20 and the party will feel it.
- The nest-mat. The chamber floor and the lower 3 ft of every wall are one continuous mat of chewed fibre, tallow, hair, and grease. It is the room's mechanism. It is flammable, it is where the swarms re-form, and it is where the Plague-Thing lives.
- Air. The warren has one draught, along the north tunnel. Any fire larger than a torch fills the tunnels with smoke in two rounds: after that, every creature that breathes ends its turn coughing — disadvantage on attack rolls and on Constitution checks — until it reaches the north tunnel or open air. Burning the room works. Standing in the room you burned does not.
- Bone drifts. Two knee-deep heaps of small bones in the chamber corners: difficult terrain, and loud, and they are the only cover in the room (half cover if prone behind one, which in a 7-ft chamber is a real tactic).
Encounter
Four swarms in the walls and a disease-spirit in the mat, in tunnels where a shield wall is impossible.
| Count | Creature | XP each |
|---|---|---|
| 4 | Gnawing Swarm | 450 |
| 1 | Plague-Thing | 1,800 |
Base 3,600 XP; ×2 for five bodies = 7,200 adjusted, a shade over the APL 9 Medium budget of 6,600. The overage is deliberate and it is not the bodies — it is the squeeze. A party that fights this in the tunnels is fighting at half speed with disadvantage, and a party that pulls back into the chamber to fight properly is fighting on the mat, which is where the Plague-Thing wants them.
The re-forming rule. A Gnawing Swarm reduced to 0 hit points disperses into the mat rather than dying, and re-forms at the start of the third round after, anywhere on the mat, at half its maximum hit points. Burning the mat stops this. Until the mat burns, the party is not killing anything, and you should let them work that out for themselves after the second re-form — then say it plainly.
Round 1. Nothing charges. The walls move, one swarm boils out of the mat behind the party's rear rank to cut the line in the tunnel, and the Plague-Thing does not appear at all — it spends round 1 inside a swarm, which is where it fights from. It is only visible to a character who succeeds on a Perception DC 14 or who sees the swarm it is riding take radiant, holy, or fire damage.
Tactics. The swarms exist to keep the party in the low tunnels and to strip concentration. The Plague-Thing never closes alone and never appears in the open: it rides a swarm, spreads conditions rather than damage, and if reduced below half it withdraws into the mat and waits three rounds. Nothing here pursues past the warren's mouth — the mat is the thing they are defending, and they do not understand anywhere else.
Traps / Puzzles / Checks
Burning the nest-mat (the actual win condition).
| Element | Value |
|---|---|
| Recognising the mat matters | Investigation DC 13, or automatic after one swarm re-forms |
| Igniting it | Any fire damage, a flask of oil, or a torch held to it for one round. It catches on a 1-round delay and then burns for four rounds |
| While it burns | The chamber and 10 ft of each tunnel are 1d10 fire damage to anyone who starts a turn in them. Every swarm on the mat takes the same, automatically, and dispersed swarms cannot re-form |
| The smoke | Two rounds after ignition, see Air above. The party has two rounds of clean burning to be somewhere else |
| Solved state | The mat is ash, the re-forming stops, the surviving swarms scatter down the west tunnel, and the Plague-Thing has nowhere to hide. It will still fight, and now it is one body alone in a room |
| Without fire | The mat can be cut and hauled clear of the chamber: twelve minutes and a Strength (Athletics) DC 14 check per person involved, in the dark, with rats. Legal, slow, and you should make it feel like a choice they made |
Exits
None. Rats have had two hundred years with everything in here. What coin there is has been chewed into the mat with tallow and hair, and a player who wants to reach into that with a bare hand may — one Constitution save DC 12 against the warren's filth-fever per attempt, and you keep the coin either way, because it is four drachmae and a bad memory, not a loot roll.
Scaling — APL 6 / 12 / 15
| APL | Adjustment |
|---|---|
| 6 | Three Gnawing Swarms, no Plague-Thing; a swarm that disperses re-forms once and then not again. All DCs −2 |
| 9 | As written |
| 12 | Six Gnawing Swarms, and add a Grave-Honey Flow engorged in the chamber that will not leave the mat but will fight anyone standing on it. Fire damage on the burning mat becomes 4d10 for the first round. DCs +1 |
| 15 | Eight Gnawing Swarms, two Plague-Things, a Grave-Honey Flow, and the mat re-grows: unburnt sections spread 5 ft per round back into the chamber. DCs +3 |
- Pacing. Fifteen minutes. The first five are the party realising the room is a machine, the middle five are the burn, and the last five are one spirit alone in the open.
- If you are behind schedule, the mat is already half burnt when they arrive — somebody came through here with a torch a day ago. Two swarms, no re-forming, no Plague-Thing, seven minutes.
- Run the squeeze honestly and then get out of it. Two rounds of 4-ft tunnels teaches the lesson. If the party is still crawling on round four, that is a grind, not tension: let the tunnel "open out" into the chamber and give them a proper floor to fight on.
- Do not let disease steal a character's session. The Plague-Thing deals conditions, and conditions on a ninth-level party should cost the fight, not the next three rooms. Set every condition here to end on a save at the end of the turn or after the encounter, and let the filth-fever from the mat be the only thing that persists.
- Table safety. Vermin in the dark, being touched by things you cannot see, and a disease that lingers. If anyone at the table is squeamish about swarms specifically, the mat can be a fungal growth and the swarms beetles, which changes nothing mechanically and helps more than you would expect.
- Clue drip. Two objects: the chewed matter in the mat is not local — there is sailcloth and tarred rope in it, which came from somewhere with ships (X16 or X11, Whisper or Trace tier); and the collapsed shaft in exit C drops bone-meal from somewhere above, which means there is a floor above this one and it is inhabited (X14, Sign — a party mapping the maze needs to know it is three-dimensional).
- Warband callback. Keres & Plague (W20) never fight for a room, they fight to keep a room unpleasant. A party who has met the swarms before should already be reaching for oil before you finish describing the walls. Let that be right.
Creature Cards
Both belong to Keres & Plague (W20) and recur across the deck, so the numbers live in the bestiary. The re-forming rule and the mat are this room's and stay here.
Shared across rooms, so the full cards live in the bestiary: Gnawing Swarm, Plague-Thing. Every mention above opens the numbers here on this page.