Pavement Art.
I love going into the centre of the City in Summer and looking at the the work of the pavement artists, some great talent there, but nothing, to me, comes near the work of Julian Beever, Beever is an English Artist and he uses a projection technique called Anamorphosis (sounds like a super pain killer to me
) I only recently heard about him although he's been around for a long time, I love his work, here's an example if you are not familiar with his work already.