'Everest' Stars Bonded Fighting 'Dangerous' Conditions During Filming

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The cast of Everest got a taste of how daunting it can be to climb Earth's highest mountain when they were hit with extreme elements.

"It was serious," star Martin Henderson told ET. "It was avalanche warnings and our sets getting buried with Sherpas having to dig them out."

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Most of the movie was shot on location in the mountains of Nepal, which gave an authenticity to the film that could not be duplicated. It also helped the actors picture the reality that their characters faced.

"We spent a lot of time together," Jake Gyllenhaal said. "I feel very closely knit with the people on this movie and the actors in particular."

Bonds were formed through the long working hours in freezing temperatures and dangerous conditions.

"I made friends on this and I know for fact that they will be friends for the rest of my life," Michael Kelly said. "I think a lot of that has to do with the fact that we really went through something together."

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"You have to come together when you're uncomfortable," said Josh Brolin, who had to overcome his fear of heights for the film. "There was enough chaos on the set and chaos in the moutains that we all came together."

Everest, also starring Keira Knightley, Robin Wright, Sam Worthington, Emily Watson and John Hawkes, is the real-life story of eight climbers who died when a freak storm hit in 1996, resulting in the worst loss of life in a single day ever on the mountain.

The adventure-thriller opens Sept. 18.