Upon triggering, half the flagstones at the characters' feet in whatever corridor or room the trap is in fall away, revealing a dark pit with no apparent bottom. Standing upon a stone seems to prevent it from falling until the character steps off, whereupon it tumbles away after a second or so. Characters must follow each other, hopping immediately from stone to stone, to get to a nearby ledge. Dex rolls or Saving throws are required for each jump. Magic or certain skills like climbing walls may help, as might throwing a rope with a grappling hook, etc. It will require ingenuity and cooperation to survive this. Optional: The darkness below is magical, and there is also a silence spell on the same area. The fall is not far, but any characters who slip into the darkness will seem like they have dropped to their doom.
Closeup of rimless pit by NASA/JPL/University of Arizona Public Domain
