Falling Portcullis

From Xanathar's Guide to Everything, page 113.

Simple trap (level 1-4, moderate threat)

Some folk who build dungeons, such as mad wizards in search of new victims, have no intention of allowing their visitors to make an easy escape. A falling portcullis trap can be especially devious if it causes a portcullis to drop some distance away from the pressure plate that activates the trap. Although the trap is deep in the dungeon, the portcullis closes off the dungeon entrance, which is hundreds of feet away, meaning that adventurers don't know they are trapped until they decide to head for the exit.


 * Trigger: A creature that steps on the pressure plate triggers the trap.
 * Effect: An iron portcullis drops from the ceiling, blocking an exit or a passageway.
 * Countermeasures: A successful DC 20 Wisdom (Perception) check reveals the pressure plate. A successful DC 20 Dexterity check using thieves' tools disables it, and a check with a total of 5 or lower triggers the trap.