For George Barlow, scaling the highest peaks on the planet has an almost magnetic allure.
The camaraderie with other climbers and an unflinching desire to challenge himself inspires Barlow to fight through the physical pain that comes with high-altitude climbing.
"You don't always feel good," Barlow said. "But inside yourself, you know you can do it."
The 40-year-old Steamboat Springs man -- who owns the Craig Subway -- is attempting to climb the "Seven Summits," the highest peak on every continent.
He's conquered five of the seven, with just Mt. Everest in Asia and Mt. Aconcagua in South America remaining.
In April, Barlow attempted Nepal's Mt. Lhotse, a 27,939-foot peak right next to Everest.
Lhotse isn't one of the "Seven Summits," but it is one of the five highest peaks on the planet.
Barlow chose Lhotse because it's always been one of his favorite peaks to look at. "It's just a beautiful peak," he said.
Barlow's trek up Everest's shorter neighbor was not a successful one.
The first few days in base camp, which sits at 17,500 feet, Barlow said he felt great.
He wasn't showing any symptoms of altitude sickness and felt like he was acclimatizing just fine.
Barlow has had altitude sickness before, so he knew what to look for.
After just three days in the camp, Barlow started noticing some signs of a pulmonary edema -- altitude sickness.
Barlow descended back down to Katmandu, hoping the sickness would go away and he could make it back to base camp before his expedition left for the Lhotse.
"I felt good about being sick actually," Barlow said.
He was confident he would beat the sickness and still climb Lhotse.
After a few days in Katmandu, Barlow felt better, but he was only at about 90 percent.
"You have to be at 100 percent," he said. "I had to throw in the towel."
Barlow made the trip home, frustrated be----cause his trip wasn't successful.
When he made it back to the United States, he got more bad news.
Mike O'Brien, one of the climbers Barlow had trekked into base camp with, had died on Everest.
Barlow had never met O'Brien before the trip, or his brother Chris O'Brien, who was also on the expedition.
But he formed a close bond with the brothers during their trek up to base camp.
High-altitude climbing means placing your life in someone else's hands, Barlow said, so life-long friendships often are built in just a few days.
Barlow is traveling to Phil--adelphia in a few weeks to watch Chris O'Brien graduate from medical school.
"When you're roped together with somebody, you create a bond that lasts a lifetime," Barlow said.
Mike O'Brien's death shows just how dangerous high-altitude climbing can be, Barlow said.
"It's a game of Russian roulette," he said. "Every year, three or four people die on Everest."
Barlow's ill-fated trek to Lhotse hasn't deterred him from trying to conquer the "Seven Summits."
This fall, Barlow is going back to Nepal to climb Mt. Ama Dablam, a 22, 494-foot peak south of Everest.
"It will be a good testing ground to see if I can get back to Everest," Barlow said.
People who have been stricken with altitude sickness once are more likely than others to get it again.
"I'm driven though," Barlow said with a smile.
If for some reason he can't make it up Ama Dablam, he may have to give up on scaling the "Seven Summits."
But that won't mean he's done climbing. "There's still plenty of unclimbed smaller peaks in the world."