The Great Jail, is the World Government's maximum-security prison for the most dangerous criminals and pirates. It is located underwater in the middle of a Calm Belt. The only way to get there one must use a water current accessible by going through the Gates of Justice located at either the Marine Headquarters or Enies Lobby. Also, the only way to safely get to the prison is to use one of the seastone lined Marine battleships as the entire place is surrounded by Sea Kings.

Entering Impel Down:
The only way to enter Impel Down is to go through Enies Lobby. Considering this is a heavily guarded area, as well as a Sea King breeding ground the waters are too dangerous for anyone, save those who have seastone coated ships. Only Marines can travel freely to Impel Down.

To break out of Impel Down is one of the most difficult things in the world. Considering the prisoner is in cuffs he/she will have great difficulty escaping alone, however it is possible to escape alone from level 1. To escape level 1 a person needs to attack a guard and get the guard's uniform. Then they can make their way out of the prison. If they wish a prisoner may interact with Impel Down Staff as long as they are disguised however this is dangerous as if you are caught you will be sent down to a level 2.

~ Those who are captured with over 300,000 experience must be sent to Impel Down.
~ Prisoners will be assigned a level according to their strength
~ Prisoners of Impel Down wear seastone shackles
~ Prisoners do not have any of their items