The Panoptichron is a mysterious palace, said to exist outside space and time, from where you can observe and have access to any reality in the Marvel multiverse.
The Panoptichron was somehow found by the Timebreakers and while studying it they accidentally damaged several realities, setting off a chain-reaction. Being pacifists themselves they got the idea to gather heroes from various realities and basically force them to fix the damaged time-lines, and that is how the Exiles and Weapon X was born.
Much later on a mission the Exiles got hold of a piece of the M'Kraan Crystal and managed to use it to teleport to the Panoptichron and take over. They now use the Panoptichron as their headquarters.