The picture is of an Escher Lithograph called "Metamorpose" (1939). The blocks create an optical illusion of changing direction, they are the same ones that you are talking about...and YES they are very good. For someone that doesn't usually take LSD anymore, 1/4 did the trick nicely. Not tripping hard, but defintely tripping. VERY VERY laughy, nice visuals, etc etc.
[This message has been edited by samadhi (edited 16 August 2001).]