Center of Ruination

Incidentally, the Center is also a ruin in itself, but that's more for the aesthetic and is carefully maintained to make sure that it stays in a state of wreckage.
Originally located in Mesopotamia, the Center of Ruination was a former home of some form of ritual combat from one of the various cultures of the ancient days. The architecture is rather difficult to place since it has rather decayed since then, and also because it was teleported to an island in the middle of the Atlantic Ocean in the 1700s.
Barring a few moments when there was no one with the appropriate technology or powers, the place was used as a meeting point for the Chaos Coalition during its various points of existence.

Type

Amphitheatre