This summer, the Spanish ski mountaineer and long-distance runner Kilian Jornet Burgada scaled Denali, the highest mountain in North America, in little more than a workday. Jornet used skis with climbing skins to ascend Alaska's 20,237-foot peak, then skied down, making the 33-mile trip in just 11 hours, 48 minutes – cutting nearly five hours off the previous mark. "The only question was the weather," Jornet says. "I knew that if I could get to the top, the record was done."

Good weather didn't come easy. Jornet and his team spent 16 days on the mountain, all but three of them in storms and fog. On the gusty morning of the attempt, the thermometer read minus 68 degrees at base camp. Jornet started skiing up the glacier with just a liter of water and an energy gel, and opted for a route that required an unroped stretch on crampons. His rapid ascent intensified the effects of altitude; at 16,000 feet the changing atmosphere and whiteout conditions hit him like a wall.

"Suddenly everything slowed," Jornet says. "I was counting my strides: One, two, three . . . to 50, then I'd start over. During the last three hours, I stopped every 10 minutes to warm my hands. I'd have to lift one ski at a time from the ice to thaw my foot, balancing on the other."

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He spent just a few minutes at the summit, shrouded in fog. "I could see nothing," he says. "But I felt comfortable." Jornet then skied down the mountain in about two hours, passing a base camp at 14,000 feet, where a small group of mountaineers cheered him on. Steve House, a Denali summiter many times over who happened to be leading a group of young climbers, was in the crowd. "He actually stopped to chat with some people and had some water before skating off," House says. "It was funny. It's like watching an Olympic runner show up at high school track practice."

Denali is one mountain of seven in Jornet's Summits of My Life project, which he plans to conclude in 2015 with a record attempt on Everest. Last year the 26-year-old ran up and down the 14,692-foot Matterhorn in just less than three hours; in 2012 he took a highly technical route across 15,782-foot Mont Blanc in less than nine hours; and in 2010 he clocked the fastest time yet on the 19,341-foot Kilimanjaro. With each new attempt, he finds his technique has improved, and his mind-set slightly altered.

"When you're young, you start out less afraid of the mountain and more afraid of your own ability," Jornet says. "The more experience you have, you get less afraid of your own ability and more afraid of the mountain. Forty or 50 percent of the time now, I'm turning around and waiting for the right timing." A few weeks after Denali, Jornet shattered another record – at Colorado's 100-mile Hardrock Endurance Run, completing the ultramarathon in less than 23 hours.