What is impel down?

Impel Down is a famous and highly secure prison in the world of One Piece, an anime and manga series. It is located in the Calm Belt, on an island known as a level 6 prison known as the "Eternal Hell." Impel Down is a fortress-like structure that consists of six levels, each level becoming more secure and dangerous.

The prison is run by the World Government and serves as a place to house some of the most dangerous and notorious criminals in the world. These inmates are often referred to as "pirate legends" and include names such as Crocodile, Doflamingo, and Ace.

Each level of the prison is designed to be nearly inescapable, with various types of security measures in place. These measures include traps, poison gas, and powerful jailers known as the "Beasts." There are also various types of cells within the prison, such as lava pits and dark, dungeon-like cells.

The prison is also known for its infamy and brutality. Inmates are subjected to torture and inhumane conditions, with many losing their minds or becoming severely weakened during their time in the prison. However, despite its reputation, several characters in the series have managed to escape or break into the prison, adding to its legacy.