Dungeon23 Room 169 (The Shallow Dark)

The 20'x20' square area of floor will descend 30' at 1' per second. When it stops at the bottom, the last 10' being in open air, this will alert the nest of 23 Huge Centipedes (AC 9 1 h.p. MMII pg.24) that thier next potential meal has arrived.