The Box in the Eye of the Storm

Also referred to simpy as "The Box" by those who know about it, the Box in the Eye of the Storm is the strongest magical prison in the world, reserved for those who pose incredible threat and cannot be contained any other way. It does not exist in our reality, but in a parallel dimension, where it can adapt infinitely to accommodate its requirements.
The exact specifications of how it contains its prisoner or prisoners depends largely on the prisoner themself. The Box can identify their weaknesses and utilise them as part of their captivity. Even if the prisoner were to escape the boundaries of their cell, which is impossible without aid from outside, they would have to make their way through many additional layers of the complicated security system.
Such layers include a disorienting magical labyrinth designed to constantly send travellers back to where they started, a heat-draining spell which will cause fatal hypothermia in minutes, layers upon layers of illusions, and a variety of conjured monsters.
Even if one somehow escaped, the Box itself is not physically in our world, and the only way in or out is suspended twenty thousand feet above the ocean (exact location classified for obvious reasons). While aircraft can fly right through the area with no problem, should any attempt be made from either side to breach the exit, a viscious localised hurricane will be conjured up.
Once a prisoner is contained within the Box, it is not usual for anyone to need to enter for authorised reasons. However two keys to the Box do exist. One lies in the hands of the United Nations Committee for Magical Issues. Such keys may be issued to individial nations' magical divisions if the UNCMI deem it appropriate and in the global interest. This decision is not taken lightly. The second key always lie with the nation who imprisoned the prisoner in the first place.
The identity of the prisoner is always strictly classified. Once a prisoner is contained, the details of their containment remain known only to those involved. Even top-level officials who would, if the same situation occurred again, be in charge of sending another prisoner, are not filled in on these details unless they become necessary.