Basic Planar Theory
When the powers of Hyerune came together to shape and form their world, they allowed six of the inner planes of reality to overlap and coalesce to form the great planar body known commonly as the World of Hyerune. All of the various Inner, or 'Material,' Planes occupy the same point in space but at different 'frequencies' of existance. Human beings who occupy the Prime Material Plane vibrate at a subconscious level on a certain frequency that matches that of their reality. If a being is able to manipulate and change this rate of vibration, they are able to shift from one reality to another thereby moving from one plane to another even though they may still occupy the same point in space.