http://www.metanamorph.com/index.php?site=project&cat_dir=3D-Pavement-Art&proj=The-Crevasse

This street artist, Edgar Mueller, creates a three dimensional illusions. It's interesting to look through the pictures of his process, to watch the way Mueller manipulates lines from the start of his process, giving his work the 3D effect. I recommend looking at some of his other projects on his website as well.