These guys are pros at being ninjas.
http://www.youtube.com/watch?v=KtdYsd_QRmc
Its actually a sport, called Parkour. I do a bit myself, but im no where near as good as these guys.
Yeah, if you wanna see the urban ninja on crack, here you go:
http://www.youtube.com/watch?v=w7fQo6zn9fs