Ok, this is kind of trippin...

You can get sort of a 3d illusion by looking at these and crossing your eyes...
http://chuckheron.pbwiki.com/Rendering

It takes some practice, but you have to cross your eyes so that the two things overlap in the middle, then focus on that... you should be able to see an illusion of depth...

I've shown to several people and they haven't had very good luck seeing the illusion, so let me know if you can see it...

(click the image or the link above to see a bunch of full blown animated versions)

The technical term is a cross-eyed stereogram..  The thing or object or 3d undulation or whatever is based on an planetary orbit algorithm that I've been playing with for years.. To make it solid, I adapted it to generate 3d models for Povray, which is a very cool open-source 3d-rendering package...  There's more about it on the link above..