Nest of Maggots

The Ujimushi no Su (蛆虫の巣, Nest of Maggots) is a prison under the supervision of the third corps (known as the Detention Unit) of the Onmitsukidō.

Overview
It is located on the grounds of the Second Division, and is surrounded by a moat. On the inside, it resembles a cave with an area for prisoners. When a Shinigami becomes a potential danger to other Shinigami and Soul Society, that Shinigami is brought to the Nest of Maggots for imprisonment, regardless if they were put on trial; this is to ensure no danger will be brought to Soul Society. All prisoners are not held inside a cell (since they cannot set foot outside the prison). The exception is the Nest of Maggots' infamous former resident: Mayuri Kurotsuchi, considered at the time an exceptionally dangerous person. Treatment for the prisoners is mostly lenient; they can walk freely and converse with one another, but the bleak setting drives many to madness. Neither the staff (called jailers) of the Detention Unit nor any other visitors are permitted to carry a Zanpakutō into the Nest of Maggots; visitors must deposit them at the entrance. This measure means that the jailers are required to be able to control the prisoners with bare hands. If a Shinigami desires to enter and is not adept at hand-to-hand combat, they may not enter. This is to prevent rebellions and escapes from the prison.

Kisuke Urahara, as Corps Commander of the Detention Unit, was once in charge of the Nest of Maggots before being promoted to Captain of the 12th Division. During a visit, he demonstrated to Hiyori Sarugaki that he is capable of subduing even the most physically powerful prisoner in the Nest of Maggots with his bare hands, which he described as a key requirement of the Detention Unit Commander's position.