It was the worst day on the world's deadliest mountain, Aug. 1, 2008. Twenty-nine climbers headed for the summit. Only 18 would return.
K2 would kill the first Irishman ever to make the summit. It would kill a 61-year old grandfather on his third attempt. And it would kill one-half of mountaineering's most adored couple, soulmates in love with each other and with extreme adventure.
Thousands have conquered Mt. Everest, but only a few hundred have summited the world's second-highest peak, K2. Death is the recurring theme on K2, a steeper, tougher, riskier mountain that draws the brave and foolish into northern Pakistan each season.
For every four climbers to reach K2's summit, one dies. And if going up doesn't kill them, then coming back down could.
"Death during decent. This mountain is notorious for this," said climber Eric Meyer, an American doctor from Colorado.
Just getting to the base can be treacherous. Thrillseekers have to spend hours winding around dangerously narrow mountain roads in Jeeps, and then endure an eight-day hike before they can even get their first glimpse of K2 in person.
Filmmaker Fredrik Strang, with his cameras rolling, was among a group of mountaineers that converged on K2 two summers ago. "Nightline" was able to obtain his exclusive footage as he documented the team's hazardous journey through the walls of ice and rock.
Strang's videos show grim warnings of how vicious the mountain can be. Dozens of memorials dot the area around base camp. In places the mountain holds the remains of fallen climbers.
"You're standing close to a leg," one climber can be heard saying on camera.
In addition to Strang's videography, details of what happened on the mountain's deadliest day emerge in "No Way Down," a book by climber Graham Bowley, who visited the scene.
Aside from shifting ice, falling rocks, avalanches and sudden storms, climbers have to adapt to the high attitude and thinning air. When oxygen becomes scarce, the brain becomes foggy and muscles chill. Their journey can take months.
The maximum amount of time a climber has to get out of an oxygen-starved death zone is 18 hours.
"When you go up, your muscles tell you, 'You have to breathe now,'" said Norwegian climber Cecelia Skog.
Skog, 36, is the first woman to climb the highest peaks on all seven continents. She and her husband Rolf Bae tried to summit K2 once before, but turned back in bad weather. Their second attempt took a fatal turn.
Skog joked that she had a hard time finding boyfriends who could keep up with her extreme hobby, until she met Bae, who proposed while they were skiing to the North Pole.
"[He got down on one knee] with his skis on," she said.
The couple was on K2 that fateful August day. They ascended quickly, but their climbing group was held up by other climbers at an especially treacherous passage known as the Bottleneck.
It was just before dark, and Bae began to feel weak.
"I gave him my oxygen and then I thought maybe he ... then he would feel better," Skog said.
But Bae couldn't recover. He encouraged his wife to continue on without him. Skog forged ahead and eventually made it to the peak of K2.
"It was amazing. It was fantastic. We could see that shape of K2, that shadow," Skog said of her experience on the summit. "We could see so far into China. It was, uh ... there was no wind, the sun was still up."