The Ethereal Plane of Atrii, home of the Implementors, is an alternate plane of existence that has specific locations that coincide with the same locations in the real world. However, the geometry and very nature of space in the Ethereal Plane is different in an indescribable way.
Those who have mastered transcendental physics can easily jump back and forth from the Ethereal Plane to the real world via magic curtains called Dimension Doors, or through the use of a Scroll of Gating. These transcendental voyagers report that solid objects from the Ethereal Plane appear only as vague outlines in our world, and vice versa.
The Plane of Atrii is also the way that Orkan of Thriff was so easily able to transport his entire village anywhere he desired in our world. It has been discovered that a transcendental traveler, upon magically entering the Plane of Atrii, can easily return to the real world via magic curtains specially designed to provide a one-way trip.