Transcript for Rock Climbing Champ's Mission to Conquer Terrifying Ascent

We are going to the top of the world tonight, with a rock climbing rock star. She's a 21-year-old ivy leaguer who is now tackling the biggest challenge of her life. A climb so dangerous, it's called the madman's journey. Can she make it? Tonight, we're right there with her. Here's my "Nightline" co-anchor juju Chang. This is by far the hardest route that I've ever attempted. About 1,000 vertical feet. And it's one of the world's hardest multipitch climbs. Reporter: Sasha lives for clichs like this. So steef, P, so remote. It's only been done by two men before and that was over a decade ago. Reporter: That they can even rattle one of the best climbers in the world. My heart is in my throat. It's too dangerous to fall. You can't fall. I'll try to be the first woman to do this climb. Are you afraid of heights? No, I'm not. I think it would be really hard to be doing this if I was afraid of heights. Reporter: At just 21, this world champion rock climber and ivy league junior isn't satisfied unless shell's on top. What are you afraid of? I'm afraid of sharks. I have small fears, but I don't like feeling not in control. When you're on that edge, you're in control of your own destiny there. Reporter: Sasha is on a mission to redefine what's possible. We're at the wall. It's one of these. Reporter: A year of planning and training, bringing her and a team of expert climbers to the Swiss alps. Sasha is the forefront of female rock climbers. She's certainly one of the best in the world. Reporter: One of her sponsors, red bull, hopes to film her attempt to climb a jacked route only a brave few have ever completed. This should be the wall with those clouds. The weather couldn't be worse. Wednesday, it rained. Thursday it rained. This is our fourth day in a row of rain. Friday, rain, Friday, rain. The weather here sucks. It was so frustrating, feeling like the epitome of cabin fever. We must get out of the house! I wasn't really sure what to do. We're looking for drier conditions. We need to move locations and chase the good weather. So, we're relocating. Reporter: So, the team takes a huge risk, setting out for an Italian island known for its rugged coast and brutal climate. I have friends who are climbers, they say, you are crazy to go there. It's going to be crazy hot. We are finally in sardinia. Almost. The route is really intimidating. So, it goes up and to the left. It's dangerous. Reporter: The new climb is perfectly named. A madman's journey. It's 1 tho,000 feet of climb iing. It's near impossible. It's actually happening, man. I get to the wall, it actually kind of all of a sudden hit me, like, what are we getting into? Reporter: So few people attempt this climb. Sasha and her partner spent days just exploring a wall reclaimed by nature. You are essential trusting your life to this person's hands. And when you think about it, it's pretty hefty stuff. Climbing is full of failure. Each success comes in really small doses. I don't want to do this. I just can't. Reporter: Every moment of desperation captured on film. You are having to really contort yourself in order to stay still and to get these shots in a certain way. And that's tough when you're up there, so, you know, these harnesses start to wear on you after awhile and you're squirming around a lot. You are -- all the blood seems to be running from your legs and things are getting numb. A lot of it happens really quickly. Somebody could fall at any moment. A piece of rock could break. Reporter: Sasha says the risks she takes on these risks r-kal cue lated and she never climbs without safety ropes, known in the climbing world as a free solo. I know how much of an impact that would be on my loved ones if I were to pass. I lost my dad exactly two months ago. It really makes you feel like life is really sacred. What's special about being here is that he's Italian. I know that he would, if he was around, pull out the map and be like, this is where the family's from, and it's nice to think that they're smiling from somewhere and happy. Reporter: After nine days of preparation -- It's coming together. Slowly but surely. Reporter: The team is almost ready. Once I try the route. Reporter: They go over the plan and Sasha's biggest fear. The fifth pitch is really mentally exhausting. Reporter: The easiest part of if climb is actually the most dangerous. Instead of falling into air -- You are bay suckly facing, like, scraping down the rock. Cheese grate down the painful surface of the wall. Reporter: One missed toe hold and she could slip 60 feet. It could mean failure or worse. My heart is in my throat and it's like -- I can't move, because I'm thinking, like, if this breaks, then I'm doomed. Like, it's too dangerous to fall. You can't fall. Reporter: Fear and uncertainty, even a dip in the mediterranean can't wash it away. It just feels so possible. But I also know that it's not certain at all. At all. So, it's been about 12 years since this route has seen another assent. And that's what we're going to try to do today. I'll try and be the first woman to do this climb. Reporter: With the camera crew in position , they begin. Edu leading on the first section. It's a really incredible feeling, when you feel like you're in the flow. There's good air. It's windy, not too windy. Perfect blue skies. It's like this moment of feeling really limitless. So far, two down, five to go. Reporter: More than four hours into the climb, Sasha decides to lead the way on the dangerous fifth pitch. It feels like free sol lowing. Your last drive, like, so many meters away. Reporter: The doubts that plague her seem to melt away. 30 meters away. Oh, yeah. Woo! I'm almost like invincible today. One more. And if I fall, I'll be falling fearlessly. Here we are, after six pitches. About to go to the last pitch. And I came over the ledge with my left hand -- we made it! Yeah! Reporte . There's Edu's face. All we could articulate is "Woo!" Are you at the top of your world. We did it. It's like -- it was magical. Reporter: For "Nightline," I'm juju Chang.

This transcript has been automatically generated and may not be 100% accurate.