Yes, Imperial Torturer, there is an oubliette. It is, however, always flooded and so when the stone (called the "stopper" or "plug") is in place it becomes a somewhat damp place to stay (or so We are told). We doubt that you would like it there, as the guards must always wear hip boots or wet suits. There is also a plethora of mold.

Emperor Rapparee, Imperious Rex          ®         His Mark