Tiny versions of them are found in specific locations throughout Impel Down.
The prison is carefully monitored all around by a Surveillance Den Den Mushi. Among these include continuous whipping, brutal beating to death, boiling cauldrons for burning and drowning, and spiked pits used for impaling. The torture chambers are used for all sorts of brutal, unspeakable acts. The cells are all made from seastone to keep those with Devil Fruit powers from escaping. Within the dark confines of the prison are various cells and torture chambers that are used for the prisoners. Along with these beasts, the prison is guarded by a force of Marine battleships.
Due to it being built within the Calm Belt, the entire structure is constantly surrounded by gigantic Sea Kings swimming below the water. Impel Down is a large submerged tower-like structure whose foundation is at the very bottom of the sea bed. 5.2.2 Miss Goldenweek's 'Operation: Meet Baroque Works'.4.3 Level Assignment and Life of Torture.
