Nagai Hideyuki uses two sketchbooks to create 3D illusions. I was thinking this may be possible to do on the street/buildings with chalk, but in order to view it correctly everyone would have to be the same height, so that probably wouldn't work.
22 Very Unique Staircases.
A super cool idea for hiding stuff. Obviously, I wouldn't be using it to hide liquor, but other stuff would be cool. :P
Batdog [ Actually a Cane Corso, an Italian mastiff breed ]