An Oubliette refers to a type of prison cell. Such a cell was a type of dungeon cell built deep underground and only accessible via a hatch in the cell's ceiling.
The prison cells at the classified Federation Starfleet asteroid were described as modern oubliettes. Like their Earth counterparts they were built deep underground. Because the facility was meant to house prisoners that could potentially use telepathy to manipulate the guards, drones were used to guard the few prisoners sent there. The drones could use holographic projectors to project images of guards, who would be controlling the drones from remote stations. (ST - The Fall novel: The Poisoned Chalice)