Scouting for a picture this evening, I passed this building on the Rancho Los Amigos National Rehabilitation Center campus and thought, what a cool building, with its unevenly shaped blocks creating curvy lines. Then I took another look, the way you're supposed to from the side, and realized that all the blocks are the same size, and the curves are just an illusion.
This is an example of the café wall illusion, in which the parallel straight dividing lines between staggered rows with alternating black and white blocks appear to be curved. (Wikipedia) The cafe wall illusion is one type of a line illusion, which uses surrounding colors and objects and our experience with perspective to use all our knowledge against us.
Click the image above, and then click again, for a larger version to better see the effect.