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Trapsmith: Collapsing Corridors

Posted In Articles, Front Page, Traps | 7 comments

opening the doorTrapsmiths only take two levels of security into consideration while working on a project: adequate and excessive. Experienced rogues can attest that “excessive” is the most common level of security.

Collapsing Corridor Trap (CR 14)

Two adamantine doors seal off a long corridor.

The adamantine doors are locked and barred (hardness 20; 80 hp; break DC 32). The lock is of superior quality (Disable Device DC 40).

Merely touching the door sets off the collapsing corridor trap:

A loud crumbling noise, originating at the start of the corridor, signals your mistake. The floor itself falls away into nothingness…

Type mechanical; Perception DC 39; Disable Device DC 39
Trigger touch; Reset none
Effect 100-ft. pit (10d6 falling damage; Reflex DC 25 avoids fall); multiple targets

Immediately, a 10-ft. square of the corridor floor falls away. On successive rounds, the floor will fall away at an increasing pace: on the first full round after the trap is set off, an additional 20 ft. of the corridor falls away; on the second round, an additional 40 ft. falls away; on the third round, the remaining sections of the corridor fall away. The trap acts on initiative count 12.

As long as there is still a portion of the corridor remaining to escape to, PCs can avoid falling down the 100 ft. drop (Reflex DC 25 avoids).

Quick PCs might escape this trap by jumping to safety (Acrobatics DC increases each round): DC 10 clears the 10-ft. section in 1st round and DC 30 clears the 20 ft. section in 2nd round. PCs can also escape the effects of the collapsing corridor by climbing (Climb DC 25).

Adequate Collapsing Corridor Trap (CR 8 )

Type mechanical; Perception DC 29; Disable Device DC 29
Trigger touch; Reset none
Effect 60-ft. fall (6d6 falling damage; Reflex DC 20 avoids fall); multiple targets

The “adequate” version of this trap features standard, locked iron doors (Disable Device DC 30) with a 60-ft. pit.

There are several magical variants of the collapsing corridor trap; the cheapest version is the shocking fall trap.

Shocking Fall Trap (CR 15)

Two adamantine doors block your progress.

Type magical and mechanical; Perception DC 41; Disable Device DC 40
Trigger touch; Reset none
Effect spell effect (maximized lightning bolt, 60 electricity damage, Reflex DC 19 for half); multiple targets (all targets in a 10-ft. square)
Effect 100-ft. fall (10d6 falling damage; Reflex DC 25 avoids fall); multiple targets (all targets in a 10-ft. square)

The adamantine doors are locked and barred (hardness 20; 80 hp; break DC 32 Strength). The lock is of superior quality (Disable Device DC 40).Merely touching the door set off the shocking fall trap.

A 10-ft.-square section of the stone floor in front of the adamantine doors is only 1 inch thick and covers a 100 ft. deep pit. At the bottom of the pit, several maximized lightning bolt traps are targeted upwards. Touching the door triggers the trap, and the resulting barrage of lightning bolts blasts through the floor, hitting everyone occupying the 10-ft. square and dealing 60 electricity damage (Reflex DC 19 for half). The destruction of the floor causes everyone occupying the 10-ft.-square section to fall into the 100-ft. pit (Reflex DC 25 avoids fall).

The shocking fall trap can easily be modified to encompass a larger area, but mechanically, this does not increase the CR of the trap.

(This post is Product Identity.)


  1. Diabolical! Love the variations!

    James Thomas

    April 6, 2010

  2. The Shocking Fall trap is inspired deviousness.


    April 6, 2010

  3. The Shocking Fall is terrific.

    I think sometimes DMs with higher-level group don’t do as much with traps as they could, but an average of 95 hp damage would certainly get a 15th-level party’s attention.


    April 6, 2010

  4. As a trap builder I’m not sure. My consideration has to do with the fact that this trap appears to be a one shot only, and after that the corridor is useless. Personally, I prefer traps that can be reset. Instead of a crumbling floor I would prefer a hinged floor that splits down the middle and opens laterally all at once. This gives my opponents (those damnable intruders!) no chance of jumping away, and it also lets me reset the floor after they are all killed on the poison spikes at the bottom.


    April 6, 2010

  5. @vbwyrde

    Trap builder eh?

    Show us what you can do!

    Scott is always looking for new traps.


    April 6, 2010

  6. My only concern are the doors– I’ve seen too many groups who would just gleefully loot those things.

    I end up adamantine plating another strong metal to avoid the problem.



    April 6, 2010

  7. Another set of great traps, Darkjoy! Keep ’em coming.


    April 7, 2010

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