Ink and pencil
Christophe Chalmette (libre-comme-lart)
Try to sit down on this chair. Perhaps you will not fall with him, if you're lucky.
More impossible chairs you can see in out photo montage section.
Artist's deviantART profile http://libre-comme-lart.deviantart.com
The image was found at http://libre-comme-lart.deviantart.com/art/chaise-impossible-119165694