Opening the chest causes the room to spin rapidly.
A DC 16 Intelligence (Investigation) check while entering the room notes an air gap in the doorway; the room is not connected to the outer hallway.
A DC 14 Wisdom (Perception) check detects various indentations in the walls. Closer inspection and a DC 14 Intelligence (Investigation) check reveal that these indentations were caused by small, sharp objects.
Small wires can be seen by the hinges on the chest with a successful DC 16 Wisdom (Perception) check, as well as the fact that the chest is bolted to the floor.
When the chest is opened, it reveals itself to be full of small, sharp caltrops. Then the room spins rapidly for 1d4+3 rounds. This causes the doors to slam shut.
All targets in the room must make a DC 16 Strength check. On a failure, they are flung against the wall, taking 2d6 bludgeoning and 4d4 piercing damage and becoming restrained.
At the start of a character’s turn, that character takes 1d4 additional piercing damage if they are stuck against a wall. If they are not, they must make a DC 16 Strength check or be flung against the wall. As an action, the target may free itself from the wall with a successful DC 16 Strength check. Movement is 1/2 speed.
A door requires a successful DC 18 Strength check to open, and slams closed immediately if not held open. However, since the room is spinning, in order to escape, the target must make a DC 18 Dexterity (Acrobatics) check. On a failure, the target crashes into the wall, taking 4d6 bludgeoning damage.
After the first round, the caltrops fly from the chest. All targets in the room take 4d6 bludgeoning, piercing, and slashing damage, with a DC 18 Dexterity saving throw halving this damage.
The trap can be disabled by cutting the wires near the hinges. This requires a successful DC 16 Dexterity check with thieves’ tools. Failure sets off the trap, but the caltrops will remain inside of the chest, as the lid is closed.