M. C. Escher, for those art rubes out there, is the grand master of the perspective based optical illusion. His architectural drawings of endless or inverted stairs have become cultural icons…selling countless calendars.
Some of his drawings appear at first glance to have hidden messages. In some cases this is a loss of knowledge of the original context (first image below). In other cases it appear to be just Escher’s tendency toward surrealism at work (second image below).