"The Impossible Elephant" drawn by cognitive scientist Roger N. Shepard.
http://cogpsy.info/perception/the-elephant-illusion-shepard/
and
"The impossible cube or irrational cube" invented by MC Escher
http://www.wikihow.com/Draw-an-Impossible-Cube
I used this mirror with two sides like a optical toy known as "Thaumatrope".
http://courses.ncssm.edu/gallery/collections/toys/html/exhibit06.htm