A dungeon with the only entrance or exit being a trap door
in the ceiling
“They aren’t torture chambers.” Grey was annoyed. “Left side is workshops. Storage rooms on the other side. That one’s full of papers. Not an oubliette in the house. I’m not Leblanc.”–p. 224
Bourne, Joanna (2008). The Spymaster’s Lady (Mass Market Paperback). Berkley Sensation, NY.
Definition from http://www.onelook.com/?w=oubliette&ls=a