Imagine a band of slightly loose, inch-wide flat nylon webbing stretched between two points: trees, rocks, Jeeps, or, if you're Dean Potter, 1,000-foot granite towers. Then imagine tightrope walking on a rubber band. That's slacklining in a nutshell. A campsite diversion in the 1980s, slacklining – walking on suspended nylon webbing – has evolved into a discipline of its own thanks to pro climbers like Potter and Timmy O'Neill, who often string lines high above the valley floor. Soon enough athletes from other sports caught on to its training benefits: It improves balance, coordination, and abdominal and back strength – without 90 minutes in a gym. And now slacklines have made their way from Boulder barbecues to Manhattan lofts.
Workout benefits aside, it's plain fun – once you realize it isn't easy; you'll fall several hundred times before finding your legs. Says O'Neill, "Anytime you are in grave danger of a tensioned line thwacking your family jewels, there's a sense of excitement and giddiness.
How to do it? First, go barefoot. Then, when you're first on the line, lean back slightly so that as soon as you step forward, you don't commit until you fully shift your weight onto the ball of your lead foot. Look to a fixed point at the end of the line, keeping your upper body still and your knees bent. Lead with the hips, not the shoulders.
More information: Most outdoor stores sell webbing and carabiners. Or try an intro kit – a 30-foot line, two tree slings, and a ratchet to set the tension [From $71; rei.com].