Tiny hole in the tower floor that would stop the crushing ceiling, useless without the key left behind above.
The escape from The Crushing Room is a tiny keyhole set in the floor. It is doubly out of reach: buried under a meter of poured sand, and useless anyway because Everly's party never found the matching key on the level above before the descending ceiling forced them to jump down.
Everly's Dwarf Mercenary sifts the sand for it with bleeding hands regardless, and Everly's Ogre Mercenary joins in and unknowingly refills the dwarf's excavation. Everly knows it is pointless and watches instead, fascinated by the hope draining out of a man who won't stop digging for a lock he has no key to.
A tiny hole in the chamber floor, hidden beneath roughly a meter of loose sand.
The false hope that occupies the dwarf's last minutes and dramatizes the room's inescapability.