Le Parkour
Le Parkour is the French "art of movement." David Belle and his friend Sebastien Foucan are credited with its creation. You need to go to their site and watch the video's. Reminds me of the urban spelunking I did as an early twenty-something.
I found this via Saul Albert (who I worked with on the Wireless Commons definition and Pico Peering Agreement). Saul wrote a story about a meeting with the Space Hijackers (see the Space Hijackers Manifesto). From there I randomly clicked on their ideas page and found Le Parkour and promptly wasted the next two hours of my day watching the movies on their website.