I recently learned about Parkour, which is kind of like Free Running, but different in that Free Running is more about flair and Parkour is about moving from one point to the other as efficiently as possible. You can do this in any kind of environment. It seems like you have to let go of your civilized conditioned mindset and go back to the way you played as a kid, just doing it. Of course it takes practiced skills and control so you can avoid injury. A lot of people who do this (they are called traceurs) mention becoming totally aware of their surroundings. You would have to in order to fluidly make decisions as to where to go and what you will do. Some people practice in more natural settings (I don't want to say wilderness, but there doesn't have to be any civilization around for you to do this). Basically, it's about becoming aware of everything you can do with your body to move from one place to another. If your interested I would highly recommend starting with safety moves, such as landing and rolls, which you can find tutorials for. I just started practicing rolls and landings today. It's really fun, and once I was getting the rolls right it was really exciting. Traceurs who do this long term do a lot of strength training to stay in shape for doing Parkour. Some traceurs talk about it being a mental/physical/spiritual thing, because there's that mind over matter thing and spiritually I think it helps get rid of a lot of hang ups which come from living in civilized society, sort of being free like a wild animal. It's so awesome.
Here's a video of a guy training in the woods with large rocks: http://www.youtube.com/watch?v=nZheyN30iuc