Impel Down, also known as the Underwater Prison (海底監獄 Kaitei Kangoku?) or the Great Prison (大監獄 Dai Kangoku?), is a government-controlled stronghold in Paradise together with Marine Headquarters and formerly, Enies Lobby. It is the World Government's maximum-security prison for the most dangerous criminals and pirates.[1] It is located underwater in the middle of the Calm Belt.[2]
Impel Down is the main setting of the Impel Down Arc.