It is the oubliette in which the Staphilinus buries the remains of his victims.
The gloomy chamber, however, is generally called an oubliette.
Do you remember the oubliette between the guard-room and the tower?
After the stench of the oubliette, it was like heaven to Hyla.
In the centre of the chamber there is an oubliette to the darkness below.
Nay, lady, I could look ...