Collapsing floors (synonyms: rotten floors, damaged substructure) are sections of ground that have either entirely collapsed, partially collapsed, or are at risk of imminent collapse. They are often used to create tension during narratives as characters pass over them or to act as a terrain hazard or obstacle in game worlds. While often these elements are floors, they may also be perilous bridges, catwalks, docks, or other structures. Collapsing floors can be found in abandoned buildings, haunted houses, ruins, dungeons, or as traps in other locations. Characters may fall through a collapsing floor either to their death or to a new unexplored area. Collapsing floors may lead to hidden cellars, cave systems, catacombs, abandoned subway stations, or other subterranean locations.

Collapsing floors in narratives can be used to symbolize a fall from grace, a journey into death and the underworld, or can be paired with an eventual return or rebirth.