Here is another installment of exTRAPaganza, our Thursday over-the-top trap series.
The floor and ceiling of this room are made of smooth iron.
When a target reaches the center of the room, the ceiling falls down. All targets in the room may make a Dexterity saving throw, whose difficulty is based on their distance to the exit.
Those that fail take heavy bludgeoning damage and are trapped. Trapped targets can move at 1/4 speed with a successful Strength (Athletics) check with a hard DC.
However, once the ceiling falls, the iron floor and ceiling begin to heat up. Trapped targets take escalating fire damage at the start of their turn each round.