Super Mario Mobius Strip
This is a mobius strip of Level 1 or Super Mario Bros. The whole level is wrapped around itself in a single surface, and poor Mario begins and ends at the same spot every time
All the elements from the level are there: every mushroom, turtle, cloud and star. They are all carved out of the surface at different heights, which looks fantastic when you have a light coming from the side, and each block casts a shadow. I can't imagine the time it actually took someone to design this.