I started slacklining (aka tight rope walking, but on a piece of webbing, not a wire) at Brooklyn Boulders this winter. I started off REALLY terrible. Just standing without my legs shaking uncontrollably was a challenge. Its a practice in balance, but also a mental game. Slacklining is one of those things that the harder you try to force it to work, the harder it becomes. It requires you to relax.
Here are some pics of badass slackliners from the interweb:
One day I want to slackline over water and plunge into the deep blue sea. However, I don't care about slacklining over canyons and dying.