Andrew Lipson and Daniel Shiu build faithful, 3D versions of Escher prints using LEGOs: Relativity, Ascending and Descending, Waterfall, and Belvedere. (Only one of those four images required any photo manipulation to create its "Escher effect" -- can you tell which one, without scrolling down to see the descriptions on each page?) Other people's LEGO adventures: a playable harpsichord, the Golden Gate Bridge, and a portrait of Catwoman.
LEGO Escher is an amazing collection of some of the more famous prints by famous surrealist M.C. Escher rendered in LEGO. There's tons more like this at LUGNET (LEGO International Users Group Network).
M.C. Escher + Lego = ? I used to make spaceships and houses with my Lego not 3D representations of famous optical illusions! [via Filepile]