Only the French could have come up with a sport this insane. You may have seen videos clips of youth in street clothes running, overcoming natural obstacles on the route with a variety of gymnastic and acrobatic moves including jumps & wall runs. It is an urban thing.

As usual, the recently maligned Wikipedia is the best reference on the web for anything interesting:

Parkour – Wikipedia, the free encyclopedia

The wildest clip I have yet seen should be on this page, if you have high speed internet.

Doug Taylor pointed me to this building jumper video page.