Julian Beever is an English artist famous for his work on sidewalks all over the world.  To call it "Chalk Art" just doesn't seem to do it.  They're optical illusions that make you wonder how it's even possible.  I call it a one-of-a-kind perspective on art.  Here's some of the things he's done.

See what I mean?  These are drawings on the sidewalk.  How he gets the depth and the illusion is wild.  Here's two pictures of the same drawing to show you what I mean.

Beever says his main goal is to get the photograph of the art with someone in it to illustrate the illusion.  Sometimes he has to beat the rain, but he usually gets it and it's amazing.  Here's one that looks like part of the sidewalk is removed.  People are even walking around it thinking there's a big hole in the ground, when it's just chalked up!

Here's a few more.  Enjoy.