Spoiler:

This is the Dark Palace, located in an alternate dimension parallel to the location of Symphonia. The only way in and out of this dimension is by the use of a secret passageway hidden underneath the God-King's throne. This passageway will lead to a large room with a giant stone slab, and a magic mirror. The mirror is made from a very ancient and powerful type of magic used to open the portal to the hidden world where the most elite train in the dark arts, and it's also a place where the true purpose of Symphonia exists.

Spoiler:

Very few people are given the right to venture to this secret Villa of the Symphonian God-King, but it is a place where fellow God-Kings may meet. This is also a place where the darkness is strongest, and all sin runs free.

If any unauthorized individual comes to this place, the evil here will consume them, and so will the very person that hides the path to it from plain sight. The God-King that rules this land has the power to summon dark entities here, if he so wishes.