(CNN) — The Trbovlje Power Station in Slovenia is home to Europe’s tallest chimney, rising 1,180 feet. Two Slovenian climbers saw it as a chance of a lifetime.

In October, Janja Garnbret and Domen Škofic became the first people to free-climb the world’s tallest artificial climbing route, installed on the chimney. They’re now talking about it to promote the documentary “360 Ascent.”

The pair were successful on their second attempt, which took more than seven hours.

“It’s definitely the most special thing I’ve done in my climbing career. It is climbing, but it’s a combination of just about everything I experienced before, just combined in one thing,” Škofic told CNN Sport.

Both are well-known competition climbers: Škofic, 26, won the lead climbing World Cup title in 2016; Garnbret, 21, has won multiple world championships and World Cup titles and is one of the favorites to win gold when climbing eventually makes its debut at the Tokyo Olympics.

Despite their expertise, the challenge was way out of their comfort zone, with both more accustomed to indoor climbing on walls no more than 90 feet high. This route has 13 pitches (or sections) and involves rope techniques different from what they are  used to.

The chimney was built in 1976. It’s been nonoperational since 2014. In 2016, daredevils climbed to the top using ladder rungs that were bolted to the side for maintenance.

The new route uses more than 800 artificial holds of the type used in climbing gyms and was designed by route setters Katja Vidmar and Simon Margon. Its most difficult pitch is graded 8b+, or 5.14a. (By comparison, the Dawn Wall route on Yosemite’s El Capitan has 32 pitches, the most difficult 5.14d.)

To reach their free-climb goal, each climber had to complete each pitch without falling or otherwise putting weight on the rope they used for protection.

Their first attempt took nearly 12 hours and both climbers fell on a number of pitches. Carrying heavy backpacks left them physically exhausted, and they realized they hadn’t brought sufficient food and drinks to sustain them.

The two regrouped and went again four days later, successfully scaling the chimney in seven hours and 32 minutes.

Reaching the top after such a grueling climb is a feeling that neither will forget in a hurry.

“When I think back now, I remember how uncomfortable it felt, how it was hot, it was cold, it was windy, it was everything,” Garnbret added.

“I also said one time that I never want to go again, that this was my last try and I never want to go again. But it was a super amazing experience and yeah, I was really happy when I came on the top.”

Although heights come with the territory for climbers, neither had ever experienced such a vertical before.

Škofic still remembers the stomach-churning feeling of standing at the foot of the chimney, looking up as the top disappeared into the clouds.

“I was more scared looking up, watching the chimney. I mean, I had huge respect,” he said. “But when I was on the wall, I kind of fell into the climbing so much that I basically forgot about the heights.”

In addition to being an exhausting physical challenge, both agreed that it tested their mental capacity just as much.

Their very safety was dependent on maintaining focus for hours on end and every mistake counts when you’re dangling on a climb like this.

Garnbret initially struggled with the technique of falling off such a surface.

Indoor walls tend to have a slight overhang which prevents climbers from smashing into the wall. The chimney didn’t provide such luxury.

“The chimney had the same angle for 360 meters. It was almost vertical,” she said. “So when you fell, you fell hard into the wall. So it’s something different […] I had to get used to the falling to just keep this out of my mind. Like to not be scared to fall.”

After reflecting on the achievement, neither has ruled out tackling a similar challenge in the future.

The Slovenian route was specifically built for the pair’s venture, but other tall outdoor climbing walls have opened to the public in recent years. Downtown Reno’s Whitney Peak hotel has a 164-foot route on an outside wall, and a four-pitch, 279-foot route opened last year on a Copenhagen energy plant.

The route on the Trbovlje Power Station. Credit: Jakob Schweighofer/Red Bull Content Pool 

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