Charlize Theron has spent three decades redefining the limits of the on-screen action hero, and with her latest thriller Apex, she takes on a new, terrifying peak – quite literally. For her, filming in the jagged wilderness of the Australian outback blurred the line between pure performance and a fight for survival. This isn’t the choreographed ballet of Mad Max or the neon-soaked stunts of Atomic Blonde. The performance required grit and bone-deep exhaustion, even as she dangled over a real boulder and was dropped on a 60-foot gorge into a crevasse.

Apex follows a grieving woman (Theron) as she sets off on a solo adventure in the Australian wilderness, until she finds she has to fight for her life in a cat-and-mouse chase with a serial killer. To watch Theron as Sasha in the wilderness is a palpable experience as she embodies a woman whose mental gymnastics are the only thing keeping her from the gorge below – the result is an edge-of-the-seat watch.

“To make it look like real climbing, you have to actually climb,” Theron tells me in a virtual interview. “You have to kick all those muscles in or it starts to look fake. What you see takes maybe 20 or 30 seconds in the movie, but it took me about 38 minutes to do. It was that hard.”

But even for a veteran daredevil, Apex presented a challenge that shook her to her core. The film’s heart-stopping centerpiece – the final climb over that daunting boulder – was born out of a terrifying reality. Theron, who admits she has a fear of heights, described her terrifying action sequence. “I was dropped on a 60-foot gorge like flat into a crevasse, and I had to pull myself up,” she explains. “They had me on one safety rope, but there was no room for them to put any [more ropes] on me to kind of help me up. I had to physically climb over that. I actually do have a fear of heights, and the fact that I just knew there was nothing there to help me was really intense.”

The result is a sequence that feels terrifyingly real because it is. Theron, who also produced the film, believes it feels real when watching because it really was. “You’re watching me get over that hump in real time, and there’s zero acting in there.”

“Getting over that last boulder on the top of the mountain was truly one of the scariest things I’ve ever done,” Theron confesses. “I would say that’s the scariest thing I did in the movie because I wasn’t quite prepared for it.”

As an adrenaline enthusiast myself and having done my first rock climbing experience last year, it is truly a test of endurance and strength. Given her fear of heights, I was curious why Theron does it – is it rewarding for her? It seems that Theron’s drive to push boundaries is deeply ingrained. “I am a bit competitive,” she says when asked, noting that she is constantly seeking that elusive “flow state” where overthinking disappears and instinct takes over, “so you are looking for that place where you’re living in it.”

Egerton also saw something in her boundary-pushing role. “It seems to me that you are most happy when you’re in that place where it kind of feels like you’re on the edge,” he says looking at Theron. “That seems to be the pattern that I saw when we were making this movie. You’re kind of never more at peace than when you’re really kind of pushing the boundary a little bit.”

He notes that her resilience isn’t just for the cameras. “Charlize has this infinite will,” Egerton tells me, his admiration for his co-star bordering on awe. “She’s a kind of unstoppable force. She has that incredible ability to have a compass that aims True North and just never deviates from it. You just would not dare f**k with her.”

She is candid about the grueling nature of the shoot, describing the grit required when the body finally begins to rebel. Theron credits the director Baltasar Kormákur for pushing her to go places she wouldn’t have gone before. “It’s only human to go, ‘Okay, I think we have it. I’m so tired, I’m sure we have it,'” Theron admits. “You need a partner that can actually go, ‘No, we don’t. I know your body hurts, but we’re going to do a few more.'”

While Theron provides the film’s infinite will, Egerton provides its unpredictable, terrifying spark. “There was this enormously challenging, physical component of it, which scared me, but was also exhilarating,” he says.

Stepping away from the classic leading man roles that marked his early career, Egerton leaned into something “really f—ing weird” for Apex, citing Gary Oldman as his creative North Star of the kind of career he wants to have. “I never really feel like [a classic leading man] is very me,” Egerton explains. “I really like things that feel like slightly weird character parts. This just felt like an opportunity for me to hopefully reach a really wide audience doing something that’s really f—ing weird.”

As the film’s antagonist, Egerton is a superhero of a different kind – one with the superpower of perspective. Theron was impressed by him, calling him one of the top actors she has ever worked with in 30 years. She describes his ability to see something from “30,000 feet in the sky” as a macro-perspective that helped anchor her during the most punishing days on the rock. “I think actors can become very caught up in their small world of just their character and Taron has an ability to really understand the scope of making something and how it comes together.”

The chemistry between the two is electric – a stripped-back, high-stakes play set against a massive, terrifying vista. Apex is really a two-hander that works because of Theron and Egerton‘s commitment to the roles.

Apex streams on Netflix Friday.

Images courtesy of Netflix.