Alex Honnold scales the toughest rock faces in the world, with just chalk on his fingers and rock shoes on his feet, hundreds of metres above the rocks below.
The 30-year-old climber started serious climbing at the age of 11, and has set a number of speed records for free solo climbing on some of the world's toughest rock faces over the past decade.
Free solo climbing is one of the most dangerous sports in the world, and with no room for error, some have died doing it.
That danger, and the very thought of climbing a rock face with no safety ropes, might seem terrifying to most people, but Honnold told Nine to Noon today that taking on these challenges was not about controlling the fear.
"I just think that I do a good job of differentiating between irrational fear and true, appropriate fear, when you are actually in danger. So the thing with all the big free solos that I've done is that I don't feel like I'm in danger. I'm prepared for them, so I just know that I can do it, so there is nothing really to be afraid of.
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"If I thought that I could fall off, then I would still experience fear, the same as anybody. There are plenty of walls that I look up at and think about soloing it and it fills me with fear, and then obviously I don't solo those routes.
"I don't need to control the fear because when I'm ready to go, there is no fear. I'm not suppressing fear, I don't feel fearful of something I know I can do. If you looked at a ladder, you probably wouldn't feel any fear, because you know you can climb up that ladder no problem, so these walls, when I'm ready for them, I look at them and I'm excited to do them."
He said the key to overcoming the fear and conquering the crock faces he ascended was preparation, on both a physical and mental level.
"The physical preparation is going up and rehearsing and memorising all the movements making sure I know exactly how to do it. And the mental preparation is visualising it and making sure my head is in the right place and I'm properly motivated and all those kinds of things.
"At the most basic level, you just have to climb your way up there like a ladder, so you identify where all the holds are - this one is for my left hand, and this one is for my right hand, and then I bring up my right foot and shift my weight over my hips and then I go to my next hold. It's very mechanical, really. You just have to memorise all these movements."
But all the preparation in the world can go right out the window when the unexpected occurs, hundreds of metres up a cliff face. When that happened, Honnold admitted he got the fear.
"I do still experience jolts of fear the same as anybody when something goes wrong like that. When I was doing a free solo on the Rainbow Wall at Las Vegas, when I got up to the spot where I was supposed to jump - and I suddenly realised there was a jump involved that I hadn't really prepared for - it was suddenly something unexpected and I thought 'oh no'. That's why I had to hesitate and work through it over time and figure something out."
Safety versus difficulty
However, Honnold said the more dangerous the climb looked, the less likely it was that something could go wrong.
"That's why several of the world's best soloists have died on easy terrain, because it's almost like it's too easy and they don't have to give it the 100 percent focus and they make one little error.
"The statistic I like to throw out is that no soloist has ever died pushing the limits of the sport, nobody has ever died doing anything cutting edge, they've only died due to trivial, little errors on easy routes. You can't say that with other sports."
Honnold's breathtaking climbs have been captured in documentaries and articles, and he recently wrote a book, Alone On The Wall, which detailed his climbing exploits.
He told Nine to Noon when people asked him when he made the decision to become a professional climber, he couldn't give them an answer, because it had been a long, slow progression.
"It's never been one moment. I think one of the keys to my success as a climber has been its gradual progression - constantly taking lots of baby steps and pushing myself a little bit further and a little bit further. There have been a few solo climbs that I did, such as soloing Half Dome in 2008, where I pushed myself further outside my comfort zone than I expected, I thought it was going to be a baby step, but it turned out to be a pretty big step for me."
He said he felt compelled to keep climbing and was almost obligated to see if he could take on the toughest challenges.
Honnold shows little sign of stopping, and said he would continue solo free climbing for some time to come.
"I don't really see a point when I will stop climbing in general. I probably will stop with the solo freeclimbing at some point, maybe I just won't feel comfortable any more because I won't have that confidence. But for now I'm still improving physically and I'm still hoping to climb harder things, so I'll cross that bridge when I come there.
"But I'm sure at some point it will just be clear to me that I don't have the hunger for it or don't have the fitness for it. We'll just see."