I've been checking out sites on parkour, an "extreme sport" originating in France in which the athletes (traceurs) run across, jump around and perform Spidermanesque acrobatics off of urban architecture. It looks, like, totally rad, dude. It's like skateboarding without the board.
Check out the gnarly vids on this dope website to see what it looks like. (Great French rap soundtracks too!)
I wonder if this has gotten any press coverage in the States? I certainly hadn't heard about it until a few months ago. The parkour community looks to be quite widespread, especially across Europe. I've found a couple websites devoted to the sport: Urban Freeflow and the UK Parkour Association.
Here is a good news article about parkour.
There is even a 2001 flick written by Luc Besson called "Yamakasi - Les samourai des temps modernes" that features Traceurs. I saw it in the video store in Japan with the tag line ７人の超人が飛ぶ！ but never got around to renting it.
Parkour takes the stuff you used to do on the playground as a kid--or running from the cops--and elevates it to an artform. All good fun, but falling off a roof must hurt a bit more than falling off a jungle gym.