ON GOOGLE EARTH, 18°S 69°W is shown perched on the southeast face of a dormant volcano called Jachcha Condoriri, protected by cliffs above and below, its crosshairs marking a bulge of igneous rock in a field of scree. Its elevation is an imposing 16,961 feet, but the surrounding terrain does not look impassably steep. To gaze at it on Google Earth is to play God, flying back and forth above a digitized, photorealistic mountainscape, spinning until you've seen it from every angle and taken in every obstacle. There could be a snowfield or two to navigate on the hike in. There's a possible couloir route between the cliffs. If bad weather rolls in, the scree slope may be the way to make a quick escape.

Zoom out and the approach becomes obvious. A quarter-mile north of the confluence, via either a couloir or an open slope that skirts the cliffs, is a false summit at 17,477 feet. Leading directly to it is a clear, treeless ridgeline with a relatively gentle angle. Zoom farther out and the world becomes ever more barren and volcano-spotted, and you see the faint outline of a jeep track that happens to bisect the bottom of the ridgeline. The track leads to a nearby village—just nine miles across the Altiplano as the crow flies—and if you zoom back in you can see its name: Tomarapi.

Tomarapi is tiny, but a Web search reveals that it is home to a new, Aymara Indian–run eco-lodge: room and board for less than $40 a night. The giant volcano lording over Toma­rapi and the confluence mountain turns out to be Nevado Sajama, at 21,463 feet Bolivia's highest peak, and the area surrounding it turns out to be Bolivia's oldest national park. Because national parks the world over tend to have transport for hire, logistics will be the easy part.

As for the approach routes to Tomarapi and to Bolivia itself, they were outlined in Greg's Lonely Planet guidebook. He flipped through it in Brazil, where he was posted as a geophysicist aboard a roving seismic-survey ship—his day job—and later that week boarded a string of buses. First from Rio to some islands off the Atlantic coast (a getaway with a local girl he'd met); then to Iguaçu Falls, at the Argentina border (where there was a mock Mardi Gras at a hostel famous for its huge swimming pool); then nonstop across the width of Argentina to the town of Salta, near the Bolivia border ("I had to go there," Greg said, "because it's Atlas spelled backwards.") In Salta, he tried to buy some soap (jabón) at a grocery store and ended up in the ham (jamón) section. Greg does not speak Spanish. That night he went out for pizza with a pack of 14-year-olds he'd met on the street and one of their moms. The next day he went on a tour of the nearby canyon country. The day after that he got himself across the border. By the time Paolo and I caught up with him, in the desert town of Tupiza, Bolivia, Greg had spent 68 hours riding public buses toward the confluence, and together we did another eight to reach the town of Uyuni, where we switched to a Land Cruiser. He rode without complaint or apparent discomfort, jamming out to his MP3 player, reading Berlitz's Spanish in 30 Days, and blithely falling asleep as we traversed knife-edge ridges above thousand-foot drops. The bus smelled vaguely of green tea—from all the local coca-leaf chewers, Greg thought. We passed eight-foot cacti, a desert funeral, and a woman riding a bicycle while holding a shovel. The driver stopped every half-hour or so to pound on the chassis with a wrench, but Greg slept through it. When he woke up, he fixed his eyes on the T-shirt I was wearing, which had a large image of a king crab.

"This being a landlocked nation," he said, "that must really freak people out." Then he went back to sleep.