Here is a variant of the Moebius Strip formed out of Escher's ants walking forever and covering both sides of the ring. Click on this small movie on the right to see the real large version.
At this site "Escher for Real" there are works of Escher that are not illusions and they did a great work showing the real side of Escher's work.
I only pity these ants that will walk forever without going anywhere but I did a post about Camus Myth of Sisyphus so "One must imagine the ants happy".