Depth

I thought this photo really shows depth because of the way the giant appears to be falling into the columns. I've always been a big fan of street art like this, because it looks so real and sometimes you really have to look at it for a while before you realize that, oh, it's on a flat surface. This one's really cool because you can see the people surrounding the piece, which makes it more evident that it's actually art and drawn on a 2D surface. Foreshortening of the giant's limbs, in particular its legs, also give the illusion of depth.