NEW YORK — While climbing Mount Kilimanjaro, as part of Kenna's "Summit on the Summit" mission, Jessica Biel got to know the 19,000-odd feet of rock pretty well. In fact, she's pretty sure the mountain is actually a woman.

"She was like this mysterious, foreboding, ominous woman. And she was hidden almost all day long, and just when you were unmotivated, and feeling like crap and uninspired and thinking, 'What am I doing here?' the clouds would part and she would peek out, and the beauty would strike you, and then you'd be inspired again," Biel told MTV News on the red carpet for the premiere of "Summit." "And she was literally, like, this woman who would pull this veil over her face and disappear, and then she'd show a little bit of herself, and then she'd disappear again. It was kind of this running joke, but I really felt that way. I felt like, 'I respect you. Please let me get up, please.' "

But just because Kilimanjaro was inspiring doesn't mean she also couldn't be positively dominating too. In the film — which debuts Sunday at 9 p.m. ET on MTV — Biel and her fellow climbers (a team that also featured Lupe Fiasco, Santigold, Emile Hirsch and a team of scientists, United Nations ambassadors and experienced mountain guides) were brutalized by freezing rain and snow, gashed and twisted on stones and dizzied by the rapidly thinning atmospheric conditions. But that was just the physical trauma. The real challenge, for Biel at least, was overcoming the mental aspects of scaling the peak.

"It was a combination of the mental and the psychological aspects of the mountain, of the slow-but-steady pace that you had to go up it, and that sometimes made your brain just want to explode, because you just wanted to get there so badly," she said. "And then you couldn't see anything at night, when we were doing our ascent attempt, and you start thinking that it would never end and you'd start to think, 'Why am I here? This is miserable!'

"But then you'd get this rush of inspiration of 'I'm not doing this for me. I'm doing this for something bigger than me, for people who don't have a voice, for people that need water around the world,' and then you'd power through," she continued. "Your mind started to play tricks on you. And then, with the altitude, you just felt so strange. You didn't know why you were lethargic, you didn't know why you were so tired. It was an intense experience."

And that bigger goal was to raise awareness about the global clean-water crisis, a problem much bigger than any mountain. But Biel was inspired, not just by her trip to the top of the world, but by the larger message the mission carries: that together, people can conquer even the most insurmountable of challenges.

"That's a part of all movements. One voice is something, but a group of voices can change the world. All grassroots movements started that way, and with the Internet and people following us and watching our ascent, it really feels like people were excited by what we were doing and hopefully were inspired to create challenges for themselves, whatever that may be, and for whatever cause that may be," Biel said. "To get involved with their community, or pick something around the world that they care about, that they feel they should stand up for. That was the idea behind this. Kenna wasn't going to stop, because he had this group of friends behind him, who were supporting him. And I wasn't going to stop, because I wanted to be there for Kenna, and I didn't want to take the group down. It was such a group mentality, and I don't think we could've done it without everyone being there, and 100-percent ready for the challenge."

Don't miss "Summit on the Summit: Kilimanjaro," airing Sunday at 9 p.m. ET on MTV. And find out what you can do to help solve the global water crisis now at the "Summit on the Summit" Web site.