Bricks
The crates are empty. Four of them have no lid. The fifth you open, revealing nothing.
Moth, Schmektor, Tut, and Renwick have not been here before... the feeling of familiarity is for Brogg, Dave FoO, and Marivhon.
Moth pulls himself from sleep and examines the stonework at the top of the door. It sounds hollow beyond, as though there is a space there. The brickwork there is newer. In the rest of the room, the stone walls are old and solid.
An overwhelming exhaustion threatens to drag you back down into darkness.