Editor's note: Art of Movement is CNN's monthly show exploring the latest innovations in art, culture, science and technology.
(CNN) -- Imagine this: Floating in freezing water for 20 hours a day, over seven excruciating days, beneath a 90-meter iceberg which may or may not collapse on you, crushing you to death.
Why would anybody to do this? To surf a wave, of course.
The man crazy -- or brave -- enough to dream up such a challenge, is Garrett McNamara. The same man who surfed the world's biggest wave -- a 24-meter monster -- off the coast of Portugal in 2011.
It would be too easy to describe the 45-year-old American as an "adrenalin junkie." Instead, McNamara's addiction to "the rush," as he so frequently describes it, is so all-consuming it's practically the life-giving blood pumping through his veins.
It's also the reason the father-of-three risks his life in one of the most dangerous, and jaw-droppingly breathtaking, extreme sports on the planet -- glacier surfing.
In 2007, McNamara became the first person to surf a glacier wave -- a wave created when a 75-meter chunk of ice broke off from a massive glacier in Alaska.
As the block of ice plummeted into the Copper River, it created a two-meter-high wave which McNamara surfed -- the first and probably only person ever to ride such a swell.
"It was the closest I've ever come to death," said the man who has surfed nine-story waves on the most rugged coastlines in the world.
"I was up to my neck in water, looking up at this 90-meter tall glacier, waiting for the ice to break off and hoping that it'll fall straight into the water -- because if it falls flat you'll be squashed under it."
McNamara spent a week camped out at the glacier, spending up to 20 hours a day in the freezing water, waiting for the ice to break off and give him the most exhilarating ride of his life.
"I wanted to go home after the first day," McNamara admitted.
"But it's fun to be the first to do something. It's a totally new experience -- no one can tell you what it feels like, what to expect."
Even as a child growing up in Pittsfield, Massachusetts, McNamara was always testing the boundaries of danger.
"My brothers said I was always the craziest, always pushing buttons," he said. "When I was five-years-old I was jumping off two-story buildings."
When McNamara was 11 years old his family moved to Hawaii, where he replaced his hobby of skateboarding with surfing -- "From the very first day, I fell in love with it," he said.
By 17, he was competing in the prestigious Hawaiian Triple Crown and for the next decades traveled the globe as part of the professional surfing circuit.
"I really just want to get beautiful barrels," he said. "You're in your own world. It's a place where time stands still, where all you can hear is your heart beat."
Big wave hunter
Then in the 1990s came one of the most revolutionary developments since the sport began -- tow-surfing.
For the first time, surfers could be towed out to the biggest waves in the world with a jet ski -- and McNamara was quick to jump on board.
"Danger is real. But fear is something we create," he said. "We create fear when we think about the future and what could happen -- I'm in the moment."
Watching McNamara in action, a tiny speck skidding down the towering face of a nine-story wave, is enough to make your stomach drop. But he remains almost nonchalant.
"If you look at the statistics, it's a lot more dangerous to ride down a highway than a big wave," he said.
"If you don't make the wave, the jet ski will come get you. In 2000 we started using life jackets, so as long as you can hold your breath under water for long enough, you're OK."
It's perhaps that practical attitude which has seen McNamara smash surfing records.
In 2011 he rode the biggest wave in the world -- a 24-meter monster in Nazare, Portugal. Earlier this year he returned to the same spot to ride another huge wave, that may have been up to 30 meters high.
"I'm looking for the rush," McNamara said. "But lately I've had a really hard time finding it.
"When I surfed the glacial wave it was mind-bending, it was the heaviest rush. But since that day I've found it difficult to get that rush in the ocean. It made me realize how comfortable I feel on big waves."
McNamara's describes his obsession with that elusive rush as "like a monkey on my back." Though he chuckles as he adds: "I think the monkey's starting to lose his grip."