Gavin McClurg is one extreme dude. Or perhaps we should say X-treme. A former U.S. Olympic ski racer and world-class kayaker, he has spent his life pursuing physical challenges that most of us don’t even know exist.

The last several years have been devoted to paragliding, the sport (not, McClurg notes, the one you did in Cozumel with your mom) where you use a portable hang glider to fly long distances, often over terrain that’s not traversable by roads. At Fortune Brainstorm E, McClurg showed the rest of us relative couch potatoes what this wacky and challenging sport is all about.

The granddaddy of paragliding races is the Red Bull X-Alps championship, which is said to be the most difficult adventure race in the world. McClurg was one of just 32 participants accepted into the race, which covers 1,000 kilometers from Salzburg to Monaco by paragliding or by foot (if the weather is bad or the wind is wrong, you’re hiking—through the Alps). Held only every two years, the X-Alps is redesigned to be more and more difficult every go-round.

In July, McClurg became the first American to complete the race (only 11% of the handpicked contestants finished). He was leading for a while, but got “swampfoot” from walking through water and had to slow down. “Eventually your feet just go numb and then you can forget about them,” he says. “It was a sufferfest like no other.”

It’s hard to communicate just how physically demanding the race is. Over the course of 10 days, McClurg hiked the equivalent of five Mount Everests and flew 1,500 kilometers, often risking oxygen deprivation because he was flying so high. He was burning 10,000 to 12,000 calories daily—which is more than he could consume (yes, you carry not only your hang glider and your camping gear, but also your food). “After day two or three you can’t process normal things. I shouldn’t have made it.” But he did—and after explaining just how horrible it was, he announced, with a devilish grin, that he can’t wait to try it again in 2017.