The shadow of this cube in different directions gives QR codes pointing to the Wikipedia articles for Kurt Godel, M.C. Escher, and J.S. Bach respectively. Also a pretty challenging print test. Note that QR codes cannot be read in mirror image, so only 3 of the 6 possible cube orientations cast a readable shadow.
via Godel Escher Bach QR Code shadow cube by SashimiTabernacleChoir – Thingiverse.
Wintermute 