This is a 3D reproduction of M.C. Escher's print "Cube with magic ribbons". This print is significant for being Escher's first drawing featuring an impossible object [wikipedia]. It's quite amazing what Escher managed to do without having the opportunity to use 3D modeling software.
This image has been rendered using the POVRay raytracer. No post-processing has taken place on the image to make the illusion work; this is the 3D scene as it is rendered by the raytracer.