When Philippe Peitit walked from one of the Twin Towers to the other in 1974, that took balls. What doesn't take balls is slacklining between two trees, three feet above the air. Don't go too crazy there, you hippie. Now, we don't doubt that slacklining is difficult. Balancing on a nylon or nylon-type rope that's not pulled taut sounds like it would be killer on the abs, and in a good way. And the mobility of slacklining is also a great one. All you need is the line and some tree anchors and you're good to go, but let's not go acting like you're risking your life walking from the base of one Palmetto to another.