The Sixth Dimension serves as a 'Multiversal Control Room' which stands at the very top of the Multiversal scale. The Sixth Dimension is the highest plane of existence and exist beyond imagination and time. This realm is for things beyond the imagination of almost all living beings, where the Multiverse was designed and set in motion. Perpetua, the one who started it all and her three sons: the World Forger, the Anti-Monitor, and the Over-Monitor are the only beings known to reside there.
When any of the four residents find themselves destroyed, they re-form in the Sixth Dimension. It is almost impossible to gain access to the Sixth Dimension. Mister Mxyzptlk, a creature from the Fifth Dimension, was only able to open a portal when the boundaries of reality had been broken, an act that took a large chunk of his energy.