What you'll encounter if you try to climb K2, the King of Mountains that terrifies even the most experienced of climbers

• K2 is dubbed the King of Mountains for its sheer difficulty and high climbing death rate.
• Climbing K2 is a complex process, but several key moments in the journey stand out.

Towering over the Karakoram range, K2 is the second-tallest peak on Earth — but also considered the planet's hardest mountain to climb.

Its summit is 28,251 feet, or 8,611 meters, above sea level, just shy of Mount Everest's height of 29,032 feet.

At least 91 people have died trying to summit K2, putting its death rate around 18%, while Everest's is around 3%, according to estimates from veteran mountaineer and climbing coach Alan Arnette.

Those hoping to reach the summit have to contend with low oxygen levels, haphazard winds, unpredictable snowfall, and a slew of terrain landmarks infamous for being difficult to navigate.

The journey up the King of Mountains is complex, but Arnette helped Insider break down the key areas of K2's most commonly-used route, via the Abruzzi Spur.

Here's what a typical climb up K2 might look like, milestone by milestone.

The Baltoro Glacier

Climbers usually start their journey from Skardu, a city in the Pakistani-administered region of Gilgit-Baltistan in Kashmir.

From there, one has to hike around 40 miles through a moving glacier, said Arnette, who in 2014 became the oldest American to summit K2.

The Baltoro Glacier runs in parallel to a series of mountains taller than 20,000 feet, and is the gateway to K2.

"In the sun, it's the most stunning scenery you'll ever see in your life in terms of mountain landscapes," Arnette said.

Climbers come across a camp called Concordia, used as a base camp for some expeditions, where they'll take a left and trek alongside Broad Peak, another 8,000-meter mountain.

Eventually, they'll reach K2's base camp proper.

Base camps

"From K2 base camp, you get a very clear view of K2 just sitting very proud right in front," Arnette said.

Mountaineers take a few days to acclimatize at base camp before hiking to an advanced base camp, which sits just at the foot of K2.

Then it's a 40 to 50-degree snow slope up the mountain until climbers approach Camp 1, where rocks start to appear.

"And that's a precursor for what you're going to discover later on," said Arnette.

Camp 1

Though it's the lowest camp on K2 proper, Camp 1 is small.

It's around the size of an apartment, with enough room for just over 10 tents, which climbers have to lash closely together to save on space, Arnette said.

"There's nothing gentle, there's nothing not steep about climbing K2," the coach added.

House's Chimney

On the way to Camp 2, climbers have to face the House's Chimney. It's a narrow, steep 150-foot crack about the width of a person's shoulders.

"It's all rock and no snow at all. You have to really make sure that you have excellent rock climbing skills to get through," Arnette said.

Most climbers use a technique called stemming, or climbing with their feet on either side of the crack while attached to a fixed rope. Some grip onto a rope ladder on the ascent.

At the top, the view opens up immediately, and you can see much further ahead, Arnette said.

Camp 2

After House's Chimney is Camp 2, which is a relatively flat area that's about the size of a small house, Arnette said.

Many tents there have been left behind from previous expeditions, and have been shredded by the wind. The tent remains are then frozen into the ground, Arnette added.

The Black Pyramid

Above Camp 2 is the Black Pyramid, or 2,000 feet of very technical rock climbing. Rope ladders are scattered along the route, and some people use supplemental oxygen along this stretch.

"You're definitely using crampons, you're in a down suit because it's very cold. It can be very windy," Arnette said. "These are very, very harsh conditions."

Arnette, who's been on 38 major expeditions, said the Black Pyramid involved the most difficult climbing he's ever done in his life.

Camp 3

Atop the Black Pyramid is a small, relatively flat area that runs for another 30 meters, and is often used as Camp 3, Arnette said.

This year, Camp 3 was used as the launch point for more than 150 summit attempts in the July climbing season.

More than 40 tents were huddled together on the slopes, veteran climber Oswaldo Freire, who was on K2, told Insider.

At least 102 people would reach the peak by the end of the season, though a dying local porter, Mohammad Hassan, was left on a summit push on the morning of July 27.

The Shoulder

Past Camp 3 is a sudden, relatively flat area the size of around two or three football pitches, Arnette said.

There, you have a full view of a massive ice cliff called the Great Serac, which juts out from the summit and looms over the plateau. Most expeditions set up their final camp here, though weather conditions this year forced climbers to remain in Camp 3 until their summit push.

The Bottleneck

A rock gully that's around 300 feet long, the Bottleneck is essentially a wall of ice and rock just after the Shoulder.

Most mountaineers consider the Bottleneck the most dangerous part of climbing K2.

It's infamous for being especially vulnerable to avalanches and pieces of the Great Serac breaking off. Ice and snow can come crashing down into the gully, funneling through the Bottleneck and killing anyone inside.

Traverse

Climbers turn left after exiting the Bottleneck, and arrive at a 50- to 100-meter stretch of steep incline at the bottom of the Great Serac.

They'll have to gingerly balance along the traverse and make their way across. When Arnette climbed K2 in 2014, it was essentially a vertical wall, and he had to navigate the traverse with his crampons pointed into the mountain, he said.

He could only hold fixed ropes anchored into the ice, and climb sideways.

"The fixed rope is a total placebo, because if I fell, the fixed rope is not going to catch me, and I would fall to my death," Arnette said.

Final Stretch

It typically takes around a maximum of 15 minutes to cross the traverse, before turning right and making an arduous climb up the final stretch — a 50- to 60-degree slope that leads up to the summit.

Some climbers take around two hours to complete this section, and almost everyone would be completely exhausted by this point. "You're dehydrated, you haven't really eaten a lot, maybe 1,000 calories per day for the last four or five days, maybe a liter or two liters of water for the last three or four days," Arnette said.

At the top, one can see dozens of mountains in nearby Pakistan, India, and China. "It's one of the most awesome, spectacular, inspiring views that I've ever seen in mountaineering," he said.

Descent

The journey's not done yet, though. At this stage, most climbers are running on fumes.

"But again, you've got to now navigate the steep slopes, and when descending, gravity is not your friend. Gravity is pulling you down at every opportunity," Arnette said.

Descents on K2 usually take several days, and it's only after reaching the slopes past Camp 1 that most climbers will know they're home free, Arnette added.

"At that point, you're completely exhausted, you've got nothing in your tanks, you're operating completely on muscle memory," Arnette said. "You don't know how to take another step, but somehow you do."

A returning climber can hope a meal is waiting for them at base camp, but Arnette said some people are so tired they can't eat, or even sleep.

"It's just a physical state, which is virtually impossible to describe. To be so hungry, so sleep-deprived that you can't eat, and you can't sleep," Arnette said. "That's climbing K2."

Arnette has been climbing mountains to spread awareness for Alzheimer's since 2009, and has completed climbs on Everest and the Seven Summits.

His memoir, "Climbing for a cause: K2 with a purpose," is slated for release in 2024.