Trap of Tightening Walls
A blank room, thirty feet by twenty, with a lever beside the door you came in by and nothing else — no furniture, no bones, no dust. The side walls are dressed stone, jointed so finely you could not get a knife in, and they are not quite parallel.
When the last of you is inside, something under the floor takes up slack, and a groove of shadow opens along the base of both walls.
DM summary. A crusher whose far door is a pressure latch: it opens when the walls have closed to ten feet and not before. The party must let the room nearly kill them, or open the machine up and stop it, and either is a real answer.
Terrain & Features
Battle map: The Clean Court — page 2, 55 × 75 ft (one half of The Grey Flags)
Draw the room's starting 30 × 20 ft walls on the clean flags — then erase and redraw the two long walls 5 ft closer each round. This trap is what a dry-erase page is for. Mark the pressure latch centre-north.
- Dimensions. 30 ft × 20 ft to start, ceiling 12 ft. The two long walls are the ones that move; they close 5 ft each per round — the room loses 10 ft of width every round — starting at the end of the round the party enters.
- Light. None built in. Whatever the party carries. If the party is running torches, note that a dropped torch in a room that is getting narrower is a problem that solves itself in an unpleasant way.
- The entry lever. A timber lever inside the door, beside the frame. It opens the entry door from within, always, no check, and it is described in the read-aloud on purpose. This room is never a locked box.
- The screw grooves. The shadow at the wall bases is a pair of iron worm-screws running the room's length, one under each wall, turning slowly.
- The pressure latch. A bronze plate in the middle of the far (north) wall, 30 ft from the door. It is a load latch: it releases only when the two walls bear on its linkage, which happens at 10 ft of separation and not one foot sooner.
- The ceiling coffers. Nine square recesses in the ceiling, 12 ft up, each 3 ft deep. The walls pass under them. A creature in a coffer is out of the crush entirely and can watch the whole thing happen beneath their feet.
- The maintenance niche. A hand-sized hatch in the south-east corner at knee height, holding the reversing dog for the screws. Whoever built this expected to service it.
Traps / Puzzles / Checks
The clock, stated plainly. Six rounds from trigger to the end of the room. Say the width out loud every single round.
| End of round | Width | What happens |
|---|---|---|
| 1 | 20 ft | The grooves open. Nothing else. This is the free round |
| 2 | 20 ft | The walls begin. Grinding, and dust from the ceiling coffers |
| 3 | 15 ft | Anything Large in the room is now pinned |
| 4 | 10 ft | The pressure latch releases. The north door swings inward, open, and stays open |
| 5 | 5 ft | Every creature still on the floor: Dexterity save DC 15 or take 4d10 bludgeoning and be restrained between the walls |
| 6 | 1 ft | Anything still restrained takes 10d10 bludgeoning. The walls stop here and hold for one minute, then reverse |
Everything lethal here is telegraphed a full round early, as required: at the end of round 4 the machine changes pitch, the dust comes down in a sheet, and the screws audibly gear up. Describe it. Nobody dies in this room by surprise.
| Element | Value |
|---|---|
| Spot the room for what it is, from the doorway | Perception DC 14 on the wall joints and the too-clean floor, or passive Perception 15. A party warned before entering gets the whole thing for free |
| Find the maintenance niche | Investigation DC 15, one action, from anywhere along the south wall |
| Reverse the screws | Thieves' Tools DC 17 at the niche, or Athletics DC 18 to throw the dog by hand. Success stops the walls where they are and they begin to open at 5 ft per round |
| Jam a screw | Any rigid object rammed into the groove — a spear shaft, a crowbar, a bar of iron. No check, and it buys two rounds before it shears. A spear used this way is destroyed |
| Reach a ceiling coffer | Athletics DC 15 to climb the wall (the joints are fine but the corner is climbable), or a boost from an ally at DC 12, or any 12-ft jump or fly speed |
| Hold the latch open | Once released, the north door is held by its own linkage and does not re-close while the walls are between 10 ft and 1 ft apart. It shuts when the room reopens |
| Solved state | Walls at 10 ft, north door open, party through it — total time in the room: four rounds |
The trick the room is teaching. The far exit rewards nerve, and the maintenance niche rewards curiosity, and the entry lever rewards caution, and none of the three is wrong. A party that reverses the screws and walks out the way they came has beaten the room; they have also not seen what is past the north door, and they should be told what they gave up.
Exits
None, and the emptiness is diagnostic: a room that crushes things and has nothing in it is a room somebody sweeps. A party that thinks about that for a moment has learned something true about who maintains this maze, which is worth more than a purse.
Scaling — APL 6 / 12 / 15
| APL | Adjustment |
|---|---|
| 6 | Walls close 5 ft per round total, not per side, so the clock is nine rounds. Round-5 damage 2d10, final 4d10. All DCs −2, and the latch releases at 15 ft |
| 9 | As written |
| 12 | Both screws are geared: 10 ft per side per round, and the clock is four rounds with the latch at round 3. Round-4 damage 10d10, final 18d10. DCs +1 |
| 15 | As APL 12, and the ceiling descends too — 2 ft per round from round 2, which closes the coffers off at the end of round 4 and makes the climb a timed escape rather than a safe perch. DCs +3 |
- Pacing: eight minutes, and it must be run at speed. Announce the width every round in three words — "fifteen feet. Go." — and give each player their turn in initiative order even though nothing is attacking. The pressure of a combat round structure with no enemy is the entire experience.
- Behind schedule? Start the party at round 2, put the crowbar in someone's pack, and let the jam buy them the latch. Four minutes.
- Tell them about the entry lever twice. Once in the read-aloud and once when the walls start. A crush room that hides its exit is a party-killer, and this deck does not do that.
- The single most common table failure is a character standing at the maintenance niche rolling Thieves' Tools while the room closes on them. Give them the round-4 telegraph loudly and let someone drag them out. If a PC dies here, it should be because the player chose one more attempt after being told what was coming.
- Table safety: crushing and confinement. This is the most claustrophobic room in the batch. If crushing or entrapment is on your table's veil list, run the walls as a closing portcullis-and-spike frame that stops at 5 ft — keep the clock and the latch, drop the final 10d10, and nobody is squeezed.
- Clue drip. Two objects: the maintenance niche's contents — a maker's tally scratched inside the hatch counting services in tens, in the same hand as the marks on every Daedalan machine in the maze (X20), and the north door's linkage, which is a counterweight puzzle in miniature and is exactly how the great gate's mechanism works, at a hundredth of the scale (X19).
- No warband here, and no wandering reinforcement. The room is loud enough that anything nearby has heard it; if you want a consequence, spend it on the next room's inhabitants being ready rather than on a wave in this one.