At first, the climbers hoped it was a robbery. At midnight on June 22, 16 men in paramilitary uniforms approached base camp below the Diamir face, the most popular route on Pakistan’s 26,660-foot-tall Nanga Parbat. Bearing knives and Russian Kalashnikovs, the intruders pulled the camp’s 12 climbers from their tents, forced them to kneel on the frost-hardened grass, and then bound their wrists with rope. “Taliban! Al Qaeda! Surrender!” the intruders yelled in broken English. Discovering a Pakistani climber who spoke the local dialect, Urdu, the attackers instructed him to ask the others if they had money in their tents, adding that liars would be punished. “If we find money you are hiding,” they said, “we will shoot you.”

Earlier that day, at the beginning of the three-month climbing season in northern Pakistan’s remote Gilgit-Baltistan province – a mountainous region where attacks on foreigners have been rare – around 50 climbers from several different groups had been making their way up Nanga Parbat. Most of the 50 were above base camp preparing for the summit, leaving only a dozen climbers at the 13,000-foot base camp. Those climbers – a Chinese-American, three Ukrainians, three Chinese, two Slovaks, a Nepali, a Lithuanian, and one Pakistani – along with a Pakistani cook now kneeled on the ground in a line outside their cluster of tents.

Chinese mountaineer Zhang Jing­chuan – who would become, by dawn, the sole foreign survivor after the gunmen killed 10 climbers and the local Pakistani cook – got a strange feeling about the deliberate manner in which the attackers rounded up passports and took photos of everyone. Instead of pocketing electronics like laptops and cell phones, he later told Chinese news media, the men smashed them with rocks. Thinking of his 11-year-old son and wife back home in Yunnan Province, China, Zhang – a compact, 42-year-old climber and four-year-veteran soldier in the Chinese Army – decided to attempt an escape. When the climbers were led to a meadow on the edge of camp, he noticed the attackers separating the lone Pakistani climber from the rest of the group. “Suddenly, there was gunfire,” Zhang said. As climbers around him were shot, Zhang dropped to the ground and began working his wrists free of the rope. A bullet grazed his scalp, causing blood to run down his face. He heard screams as the attackers walked down the lines, shooting climbers in the head. Jumping upright, Zhang knocked over a nearby attacker and ran barefoot into the night as shouts and gunfire erupted behind him.

Located along Highway 35, a road linking Pakistan’s Gilgit-Baltistan district to the rest of the country, Nanga Parbat is the most accessible and affordable of the world’s highest peaks – only a day’s drive and a 15-mile hike from the capital city, Islamabad. “The conventional opinion has always been, once you get out of the big cities and into the mountains, you’re safe,” says Doug Chabot, a veteran climber who has made nine expeditions to the country. But the Nanga Parbat massacre – the country’s worst terrorist attack against foreigners in a decade – indicates Sunni extremism is spreading toward the country’s isolated Karakoram Range, a Shia stronghold historically friendly to foreign climbers. After the attack, two separate extremist groups claimed responsibility: Jundallah, a group notorious for the massacre of 18 Shia pilgrims in 2012; and the Pakistani Taliban, who stated the killings were revenge for the death of their deputy commander, Wali ur-Rehman, who died in an American drone strike on May 29. According to the Pakistani climber who survived the attack, the gunmen also claimed to be avenging Osama bin Laden’s death.

Accustomed to life-threatening risks, climbers have long braved Pakistan’s political instability to scale its world-class peaks. Five of the world’s 14 highest mountains are found along the country’s Karakoram Range, including K2, second in height only to Everest. “Take a mountain as steep and beautiful as the Matterhorn, make it 10 times bigger, and then you have the Karakoram,” says Steve Swenson, an American who has made 11 expeditions to Pakistan. “The climbing requires skill and expertise at the highest level. You can’t hire people to drag you to the top of these peaks.” Last January, in an effort to prop up northern Pakistan’s adventure tourism – an economic lifeline for villages in the rural mountains – the Pakistani Ministry of Tourism offered a 40 percent discount on licenses for climbers. Nearly 50 foreign climbing groups applied for climbing permits, an increase from 34 groups the previous year, indicating alpine tourism was on the rise. Nine licenses were issued for Nanga Parbat.

Among Pakistan’s mountains, Nanga Parbat has long had a fearsome reputation. Sixty-nine climbers have died on its slopes, and there have been only about 350 successful summits, making it one of the world’s most dangerous high-altitude peaks. Receiving more snowfall than the Karakoram, Nanga Parbat has frequent avalanches. In the 1930s, two German expeditions attempting the peak’s first ascent lost 26 men, prompting English climbers to dub it the Killer Mountain.

After sprinting 100 feet, Zhang Jingchuan came to the edge of a cliff and jumped, falling onto a gradual slope and rolling into the shadows of a ravine. “I didn’t know how high the cliff was,” he said, “but I preferred to jump to my death.” Overhead, Zhang saw attackers looking down into the darkness. He heard shouting: “Allahu Akbar!” “Osama bin Laden Zindabad!” Then silence swept over the mountain. Barefoot and wearing only thermal underwear, Zhang hid behind a block of ice, fighting off hypothermia. An hour after the attack, he decided to return to camp. A faint light glowed on the far side of the tents – the attackers were still there. Remaining out of view, he crawled to his tent, donned his jacket and boots, and found an undamaged satellite phone. Hiking to safety above base camp, he called a local emergency line and waited. As the sun rose, a Pakistani military helicopter arrived and Zhang descended to base camp. The attackers were gone.

In the week following the attack, the Pakistani government suspended the chief secretary and inspector general of Gilgit-Baltistan and launched an investigation. “It was an attack on Pakistan, not just on our foreign guests,” Interior Minister Chaudhry Nisar Ali Khan told reporters. Pakistani officials sent investigators to the region and mandated that foreigners not travel without security. Provincial police soon identified 16 suspects, arresting three of them by early July in the 20,000-person town of Chilas, located at the base of Nanga Parbat. But the damage has been done. Manzoor Hussain, president of the Alpine Club of Pakistan, stated the attack will be a “fatal blow” to tourism in the region for a decade or more. While Pakistanis living at the base of Nanga Parbat have loudly condemned the attack, their livelihoods are now endangered. “It’s what you told your family could never happen,” says Matt McCormick, an American climber who canceled a late-summer expedition to Pakistan after hearing the news. “Of course, our outfitter is saying it’s still safe for us to come, but how can we really know?”

Four days after the attack, Zhang stepped off a plane in Urumqi, China, and hugged his wife. She cried on his shoulder. They then boarded another flight to their hometown of Kunming. Wearing wraparound sunglasses and a baseball cap, Zhang landed and embraced his son. When a reporter asked the boy how he felt, he said, “My dad is a hero.”

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