From Pathfinder Adventures: Troubles in Grayce, which isn't enabled.

Unstable Floor

HAZARD 3

Stealth +10 (trained)

Description An unstable section of limestone crumbles under the weight of anyone who steps on it.

Disable DC 20 Engineering Lore, DC 20 Mining Lore, or DC 23 Survival to determine the exact extent of the unstable ground and to optionally cause it to collapse safely into area A2 below

Deeper into the Darkness

Trigger A Small or larger creature walks onto the weak limestone

Effect The ground collapses, and the triggering creature falls 15 feet into area A2 below. The creature can try to Grab an Edge to avoid falling, otherwise the fall inflicts 7 bludgeoning damage plus an additional 4d6+3 bludgeoning damage (DC 23 basic Reflex save) from falling rubble.

Pathfinder Adventures: Troubles in GrayceORC