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Meru is as much about sanity as it is about alpine rock climbing (also known as big-wall climbing). Climbers and their loved ones face extraordinary risk and loss, suffer occasional catastrophic injuries, and are continuously yanked between their ambition and their common sense. Non-climbing viewers might wonder why they do it at all.

Part documentary and part North Face ad, Meru follows three expert climbers—Conrad Anker, Jimmy Chin, and Renan Ozturk—as they attempt to tackle the Shark’s Fin route of the titular mountain, a spike of granite in India that has a reputation for being unclimbable. Anker, the most experienced of the group, is the one who put the bug in the others’ ears; you can nearly hear “unclimbable” echoing through their brains as they attempt to conquer Meru in 2008.

What the men predicted would be a seven-day adventure turned into a 20-day failure: After a prolonged snowstorm and diminishing rations, the trio had little choice but to head back down, though they were only 100 meters from Meru’s summit. They agreed not to attempt the harsh and seemingly impossible climb again.

But then, you know, stuff happened. Life got boring or, in Chin and Ozturk’s cases, nearly snuffed out, making a second chance even more attractive. With Anker, they decided to go for another try.

Ozturk’s decision seems especially bewildering; he risked a stroke after a serious injury. Chin and Anker very reluctantly allowed Ozturk to make the climb with them. As Jon Krakauer, author of Into Thin Air, laments here, “No. No! That’s not right.”

Meru is full of such decisions, ones that would make most sensible people hit the brakes. Footage of the team members’ previous climbs, particularly one free solo climb up a vertical wall by Ozturk, seem designed to stop the breath and speed up the heart. And that’s not just because of the inherent danger of each outing: Chin’s and Ozturk’s cinematography offers spectacular views of mountains and amazing light shows otherwise known as stars. Such beauty is so magnificent on a screen, viewers might almost understand why climbers tempt fate to see it in person.

Almost. These guys aren’t only toying with their own lives. Anker has a wife and three kids (and his wife has already lost a husband to climbing), Chin lives with his sister and her children, and Ozturk has a partner whom he conveniently neglected to inform of his second shot at Meru. Krakauer interprets Anker’s thoughts about this risk on their first climb in ridiculously casual terms: “I cannot die now, because then I’ve really blown it for my wife and kids.”

The film offers up a few other understatements, among them “Climbing is a really dangerous sport” and “[Chin] was really messed up” after a near-death experience. As much as each man defends his choices, it’s difficult to understand the mindset unless you’ve been gripped with such obsession yourself. Sleep in a tent staked to a vertical mountain wall? Possibly destroy your extremities with frostbite and the rot that comes from an always-moist environment? The glory and sense of accomplishment don’t seem like sufficient justification.

Even so, Meru is an enthralling experience if you can accept that this most extreme of extreme sports is a calling for some that can’t be ignored. As Krakauer puts it, “I have to do it, or else I’ll go fucking crazy.”

Meru opens Aug. 21 at Angelika Film Center, E Street Cinema, and Landmark Bethesda Row.