The 22,834-foot Mount Aconcagua in Argentina one of the most accessible of the highest peaks in the Andes.
Day 6: Base Camp (elev. 13,800 ft.)
"There are lots of reasons to feel shitty up here," said Dave Hahn, soon after we'd arrived at Plaza Argentina. We had just completed the three-day, 24-mile trek to Base Camp, finally reaching a small tent city erected in a dusty bowl of scree at the end of a lateral moraine. Bustling with climbers and mule trains from down-valley, the camp serves as the jumping-off point for the two Polish Glacier routes up Aconcagua's eastern flank: the Polish Traverse, which we would be attempting, and the more difficult Polish Direct.

My particular brand of shittiness took the form of a mild, throbbing headache, a seemingly unquenchable thirst, loss of appetite, and some mildly alarming digestive issues. Hahn assured us that he was going through the same thing. "It's all part of a conversation with my body to figure out if I'm acclimating properly. There are no tricks." A ski patroller in Taos when he's not guiding, Hahn specializes in these sorts of mini-lectures, at once didactic and reassuring.

There were three other mortals on the trip, but even they had more high-altitude experience than I did. Clark Vautier, a marketing consultant from L.A., was the most experienced climber, with Kilimanjaro, Elbrus, and Denali already under his belt. Kelley Maybo, a superfit all-around outdoorswoman from Sun Valley, Idaho, had been up Rainier five times and once topped out on an 18,996-foot Ecuadoran volcano. And Andrew Turner, who heads up the First Ascent effort for Eddie Bauer, had, a couple of months earlier, hit 19,000 feet on nearby Cotopaxi with these same guides.

From Mendoza, where we savored fine malbecs and thick steaks with the relish of the condemned, we drove to the ski resort of Penitentes, at just under 9,000 feet. We unpacked, shed some gear, and repacked for transport to Base Camp with the help of 20 mules. The first few days had the feel of a dress rehearsal for what was to come, and the guides were watching us closely, taking note of how we responded to advice. During one of our breaks, Peter noticed me walking around. "We have a saying," he told me. "Never stand when you can sit, never sit when you can lie down."

On the third morning we got our first clear look at the mountain. Aconcagua – which means "stone sentinel" – loomed at the end of a long valley, massive and cloaked in snow. It was first climbed in 1897, but an Incan mummy discovered high on its flanks proves its lure preceded that by 500 years. It was perfectly framed by the valley walls on either side of us, a gleaming white hulk with a vapor trail whipping off of its rounded top. Everest speed record-holder Lhakpa Gelu Sherpa has said the wind on Aconcagua – the viento blanco – is even stronger than in the Himalayas, and our relatively benign route up its eastern flank belies its grim death toll. Routes on its south side are some of the deadliest in the world, and the final resting place of roughly a dozen corpses. Indeed, its bite is far worse than its bark.

As we neared Base Camp, green shrubs of the lower valley yielded to a moonscape of dust and rocks – a reminder that ascending to these heights is deeply unnatural. "Look around: You see anything else alive up here?" asked Peter. "If you feel normal up here, there's something wrong with you." One of the keys to success, he told me, is "self-care": looking after our bodies, staying hydrated, and dealing with small problems – blisters, sunburn, a chafing hip belt – before they snowball into larger ones. If we needed any further motivation to take the mountain seriously, some sobering news brought the point home. Just days earlier a storm had stranded four Italian climbers and their Argentine guide near the summit. By the time rescuers reached them, the guide and one climber had died. The risks had certainly been brought into sharper relief, and, as Peter reminded us, "We've still got 9,000 feet to go."