Nature of the Island
The island is very mysterious. It contains some of the only remaining ruins of the Ancient Ones: the Cave of Trials, where the Creation Rune is kept, and is also a temporary gateway to the Enlightened Plane.
The island phases out of the Material Plane and remains in a planar "limbo" until an individual chosen by the Creation Rune finds it. It then shifts into the Material Plane, but is still not visible except to the chosen one and his/her accomplices.