Impel Down, the world's number one prison.
Located in the Calm Belt in the first half of the Grand Line, it was under exceptionally tight security.
The prison held all kinds of dangerous criminals. It was an eerie, terrifying place, guarded by all sorts of monstrous jailers and monitored by visual Den Den Mushi.
Impel Down was a colossal, tower-shaped structure that sank into the sea, with its foundations on the ocean floor. Since it had been built in the Calm Belt, it was surrounded by enormous Sea Kings, and a fleet of Navy warships protected it.
The dark prison contained all sorts of cells and torture chambers for the inmates. The cells were made of Seastone to keep Devil Fruit users from escaping.
In addition, the seafloor outside the prison teemed with enormous Sea Kings, earning Impel Down its reputation as an "impregnable fortress."
Ever since Impel Down was established, no prisoner who entered had ever managed to escape.
That was why it was known as the world's number one prison.
To this day, many people didn't understand why the Navy captured pirates instead of executing them, wasting untold manpower and money to build such a massive fortress.
In truth, Impel Down served a unique and essential purpose.
Its primary purpose was deterrence. In other words, the Navy locked away notorious Great Pirates where they would never see the light of day. This form of punishment was more terrifying than death.
Sometimes death wasn't frightening. What was frightening was suffering with no hope in sight. The moment someone set foot in this place, it meant a lifetime of isolation, accompanied by loneliness and despair. And the torment in Impel Down was beyond imagination.
Even notorious pirates were locked away here with no hope of escape. To other pirates, they