Locking-Lidded Pit Trap

The floor ahead is rough and uneven.

The floor is stone-covered plaster or flimsy wood concealing a 30-foot-deep pit. Placing more than 300 pounds of weight on the floor (typically by two or more Medium creatures walking on it at once) triggers a Critical Failure. The pit can cover any area of floor, from a 5 by 5-foot pit blocking a narrow hallway to a 50-foot-wide pit that fills an entire room.

There’s a 25 percent chance that the pit contains the remains of previous adventurers, along with a Minor Treasure.

This pit has a weighted or spring-loaded cover that opens like a trap door or swings on a pivot. Once a creature has fallen into the pit, the cover automatically resets and locks to prevent the creature’s escape. While the pit is locked, it can’t be triggered.

Lock. A creature outside the pit can make an Investigation check to find the hidden lever, loose brick, or catch that locks or unlocks the pit’s lid. A creature that makes an Engineering or thieves’ tools check can lock or unlock the pit. Only creatures that can reach the pit’s lid can attempt this check, and the check is made with disadvantage if the creature can’t see (if they are inside the lightless pit, for example). A creature can make a Strength check to break the lock and push open the pit’s lid. The pit lid is an object with AC 20, 40 hit points, and immunity to poison and psychic damage.

Exploration. A Perception or Investigation check reveals that the floor is unstable, or that there are no signs of travel through this particular area. Probing or tapping the floor above the pit reveals that the area below is hollow.

Keeping Clear. Once discovered, the pit can be bridged or circumvented. The party can travel over the pit one character at a time. Only a Large creature or one wearing heavy armor triggers it on their own.