"I try in my prints to testify that we live in a beautiful and orderly world, not in a chaos without norms, even though that is how it sometimes appears. My subjects are often playful; I cannot refrain from demonstrating the nonsensicalness of some of what we take for irrefutable certainties. It is, for example, a pleasure to deliberately mix together objects of two and of three dimensions, surface and spatial relationships, and to make fun of gravity."
-- M.C. Escher
You can view the pictures chronologically, or in reverse chronological order.