Dec. 2, 2007 -- For centuries, Sherpas have lived on the roof of the world, guiding climbers and carrying gear to the lung-searing heights of the Himalaya Mountains.
But when a 10-year civil war scared tourists out of Nepal, a new generation of these hardy porters and guides, members of an Asian ethnic group of Tibetan descent, came down from the mountains.
Now, they test their stamina and courage across a different sort of breathtaking terrain — Manhattan rush hour.
"I used to drive in Nepal," Tsering Norbu Sherpa, a cab driver and former climbing guide, who came to New York in 1998, told ABC News as he sped down Manhattan's Park Avenue. "But not at this pace and with this many lanes."
Some would consider Tsering mountaineering royalty. He's the grandnephew of Tenzing Norgay, the man who, with Sir Edmund Hillary, was one of the first to conquer the world's highest peak, Mount Everest. In his younger years, Tsering taught at the Himalaya Mountaineering Institute, and climbed up to 18,000 feet.
But now, Tsering is part of a growing community of Sherpas in New York City. Outside of Nepal and India, New York is now home to the largest population of Sherpas in the world, with about 2,5000 Sherpas living in the five boroughs, according to Outside magazine. Many, like Tsering, make their living driving cabs.
"Climbing was in my blood," Tsering said of his past adventures.
But "after getting married and having a kid," he added, "I stopped extreme climbing for my own safety."
Now he navigates the stone and steel canyons of Manhattan, working 12-hour shifts, six nights a week, in a job that severely tests his Buddhist serenity.
"It's crazy, I've seen a lot of weird people," Tsering said from the driver's seat of his yellow cab sedan. "That's why I call this job a good, bad, and ugly job.
"The worst thing," he added, "is people having sex in my car. It's such disrespect."
Christian DeBenedetti, an Outside magazine writer who spent much of this year among New York's Sherpa community, says many Sherpas struggle to adapt to their new home while clinging to their Eastern culture.
"The chance to move to America is a very difficult choice," DeBenedetti told ABC News. "They're caught between two worlds."
But, he added, "even if tens of thousands of people came and climbed those peaks every year, it wouldn't generate the kind of money that Sherpas can make here, working as cab drivers."
Sherpas in New York face other costs. Tsering has a work permit, but worries that if he leaves, he won't be allowed back into the country. Until he receives a green card, he will not be reunited with the 10-year-old daughter he was forced to leave behind in India, 10 years ago.
"There's a saying, 'if you want to achieve something, you have to sacrifice something,'" said Tsering, who keeps a small Buddha statue on the dashboard of his car. "I guess that was part of my sacrifice."
With that sacrifice, Tsering denies himself simple New York pleasures, like the view from the city's tallest skyscraper.
"None of those tourist places, because I'm saving it for my daughter," said Tsering, of never having been to the top of the Empire State Building.
"When she comes," he said, "we'll go as a family."
For more information on Sherpas in New York, click HERE.
ABC News' Bill Weir and Christine Brouwer contributed to this report.