“Meru” opens Friday at Sundance Cinemas. R, 1:27, three stars out of four.

“Meru” opens with a shot of three of the world’s best mountain climbers, sleeping in a giant bag hanging off the side of a cliff thousands of feet in the air. You don’t see that on the cover of Outside magazine.

While “Meru” has jaw-dropping visuals to rival that of fictional mountain climbing films like the upcoming “Everest,” it has a lasting impact because of how it digs into the hard work of climbing, and the psyches of those willing to to devote their lives to. Co-directed by legendary climber Jimmy Chin and Elizabeth Chai Vasarhelyi, “Meru” brings us closer than any other documentary to understanding what it’s like to be up hanging out the side of a treacherous mountain. But the more I understood what it was like, the less I understood what drove people like Chin to go back up there again and again.

That’s especially true in the case of Meru, a formidable shovel-blade of a peak (nicknamed “The Shark’s Fin”) rising 21,000 feet out of the Himalayas. Nobody had conquered it, but in 2008 Chin and his climbing partner Conrad Anker, along with relative newcomer Renan Ozturk made their ascent. They made it within 100 feet — 100 feet! — of the summit, but had to turn back or risk severe exposure or possibly worse.

In interviews, you can see how the close call gnawed at the three men. Despite the grueling work of climbing Meru, where they might make 200 feet of progress in a single day in the most formidable patches, they start making plans for another climb in 2011.

And then, in ways that seem like only-in-a-movie scripting, Chin and Ozturk both experience near-death calamities; one comes out of okay but clearly emotionally shaken, the other is severely incapacitated and has to go through months of recovery. Add to the grief that Anker is carrying at the death of his mentor and the death of his former climbing partner, and all three men face Meru carrying more weight than what’s in their packs.

It’s that psychological depth — aided by wonderfully insightful commentary from “Into This Air” writer Jon Krakauer — that pushes “Meru” beyond the traditional real-sports documentary. We really come to understand the trust that develops between climbers, the importance of a mentor relationship, the bond that comes not just from scaling a mountain but scaling it as a team.

With much of the footage shot by the climbers, “Meru” whips up moments of tremendous suspense — I was on the edge of my seat on that second climb, even though the interviews with all three climbers would seem to suggest everything turns out okay. But the film also gives you something to carry with you after that last sigh of relief.