If you are not following Fascinating LEGO Model of the Day then you should. This one is from a couple of days ago. The special feature in this set of 5 different creations and photos by Blixe63 on Flickr are the optical illusions of M.S. Escher. I am told that, "No, these are not photo-shopped." Link: http://www.flickr.com/photos/35385165@N05/tags/mcescher/
(Via: http://lmotd.blogspot.com/2011/01/more-escher-esque-illusions.html)