Dungeon Master's Guide
Simple Trap, Deadly (1st–4th Level)
This trap uses a trip wire to collapse the supports keeping an unstable section of a ceiling in place.
Trigger. A creature that steps on the trip wire triggers it.
Effect. When the trap is triggered, the unstable ceiling collapses. Any creature in the area beneath the unstable section must succeed on a DC 15 Dexterity Saving Throw, taking 22 (4d10) bludgeoning damage on a failed save, or half as much damage on a successful one. Once the trap is triggered, the floor of the area is filled with rubble and becomes Difficult Terrain.
Countermeasures. A successful DC 10 Wisdom (Perception) Test reveals the trap. A successful DC 15 Dexterity Test using Thieves' Tools disables it. A character without Thieves' Tools can attempt this check with Disadvantage using any edged weapon or edged tool. On a failed check, the trap triggers.