Stereographic Photography

This is a topic that I've always found interesting, since I had to practice a technique similar to this when I was younger (to strengthen my eyes, or something, I think). Basically, you take two very similar pictures, place them side by side, and cross your eyes until they merge. The result is what appears to be a 3D image. This example, from this site, is my favorite.

Update: my apologies to those of you who looked at this post and thought I was smoking crack. How are you supposed to cross your eyes and overlay two images that are lined up vertically? I've resized them to line up correctly. Sheesh!