Inside his helmet this paddler's world is almost silent. The only sound is his own rapid breathing. He's hyperventilating in fear and anticipation of the moment when he must take a final lungful of air. An icy wind blows spray onto his visor and hisses across the flow as gravity tugs him ever faster to the brink. Locked into his own surreal, widescreen reality, at the edges of the slot of his vision, Baker sees his paddles dipping left and right, as if operated by remote control. Lining the cliff edge, groups of tourists, freshly disgorged from packed coaches, stand aghast. In a land punctuated by spectacular falls, this is northern Iceland's answer to Niagara Falls; Godafoss (north Iceland), "Waterfall of the Gods".

"Look," someone says, pointing. "A crazy man is about to kill himself." What Baker cannot see ahead is the reason the tourists have come; great slabs of gunmetal grey water turning to jade as they career over the 100m-wide arc of the horseshoe-shaped falls, tearing themselves into a lather of foam and spray as they tumble in the maelstrom below. What the tourists don't know is that this is Baker's fourth descent of the falls today. It's just "another day at the office" for the world's top extreme kayaker, making a film for his sponsor Red Bull. What appears to be sheer folly has actually been planned to the last detail.

The film crew, positioned strategically, have safety lines and throw-bags at the ready in case Baker loses his paddle or is knocked out of his kayak. Just downstream there's another "killer" falls, slashed and spiked with daggers of rock, sharp enough to remove an arm or take the belly out of a kayak or swimmer. On a small rocky outcrop, 50m from the bottom of the falls, sits Baker's last line of defence  safety kayaker, Ant Perkins, himself a formidable and experienced paddler, ready to dash to the rescue if need be. "On the way down every possible emotion goes through me.

Fear and trepidation at the top. Focused on the way up to the edge. On the way down, I'm analysing everything that's happening to me. You live on your instinct, reacting instantaneously. Out of the corner of my eyes I can see I'm falling with the droplets of water; they're separating on the way down and atomising into spray. I'm watching the landing angle, making sure it's just right " lean back, lean forward to adjust. Then it's just amazing euphoria resurfacing and being in one piece. This absolutely focused, huge adrenaline rush burning absolutely huge amounts of energy.

Not surprisingly it doesn't always go to plan. His "last" nearly came in 1997, just a year after his death-defying Guinness World height Record free-fall drop of 19.7m (~64'') at Aldeyjarfoss (north Iceland), a plume of meltwater cascading over black basalt cliffs and fed by the largest ice cap in Europe. This time, though, his ambition was the previously untried Thjófafoss (southwest Iceland), the "Waterfall of Thieves". Its historical reputation as the place where local tribes once hurled pilferers and rustlers to their death was too big an attraction. With four times the flow rate of Godafoss, it would have been a convenient and reliable place of execution. The recirculation at the base of the falls, churning water spun by the massive torrent from above, would have been guaranteed to hold them in a lingering death roll until they drowned.

Since 1996, Baker has made around ten trips to Iceland assessing the potential of its hundreds of waterfalls and rapids. Because of the large ice caps and the volume of meltwater which swells the rivers in summer, the incredibly rugged landscape of the island offers some of the world's greatest potential challenges to the extreme white-water paddler.

"It's such an unregulated, unspoilt country," explains Baker. "I can be totally on my own here without anyone telling me what to do. People aren't so territorial. No fences or signs saying keep out or come and pay your 50p to look at the waterfall. I just feel that I'm out here in the raw, real wilderness as the island was created." Surviving in practice is what has set Baker's 20 year career above the short-lived ranks of hotheads and the hopelessly optimistic.

"It's not how easy you can make something," opines Baker. "It's about dealing with what you're presented with." On the fateful day at Thjófafoss, he was presented with a film crew, multiple cameras trained on what the director believed would be the best angle for a descent. "I decided to run a line that was borderline and that was my mistake," he confesses. "Almost from the moment I left the top I knew that it had gone wrong. I felt the rocks scrape on the bottom of the boat. It just dug into the hull and flipped over; went too vertical on a line that wasn't forgiving enough to get away with." Baker crashed into the water right under the main flow. "After maybe ten seconds the kayak and I came up as a unit. Just for a fraction of a second I thought, "I'm free". I exhaled to take a breath, but as I let that breath out I got hit by the jet. It was like a water cannon really, and I went down.

You just feel the power of being hit by a chunk of water that thick falling from that kind of height. I was hammered down below the surface. Everything just went dark. I felt like a ping-pong ball under a tap. I went so deep. I had no breath in me and I just thought, "I'm going to pass out." My eyes had begun to sparkle and my vision started to close in. I kicked the boat off my legs. I knew I had to bail out before I passed out, otherwise I knew I was going to be trapped underneath the jet and I was going to die.

In aerated water, a buoyancy aid is almost useless. Free from his kayak, Baker felt himself sink like a stone, rocketing down from the surface. "My chest started to flatten. It was like the weight of a car. I felt all my ribs cracking. I was spinning around and it was black, absolutely black down there. I expected to hit the bottom of the river really hard. I didn't know which way was up. Anyway, there was no point in swimming. I remember thinking, I haven't said goodbye to anybody, that dying wasn't supposed to be like this. I hadn't prepared for death at all."

Meanwhile, his friends on the bank were anxiously timing his crash-dive. How long could he survive? "I just wanted to take a breath. The pain was quite incredible. I had this throbbing headache and tunnel vision. Then I began to see the light above. I didn't know if I was going to last to get all the way up there," Baker recalls. Suddenly he was shocked to find himself back at the surface. "I had almost no vision left at all. I remember taking three or four breaths one after the other without letting anything out, just to re-inflate my lungs.
I felt amazing. Like being re-born." The video confirmed he had been submerged for well over a minute with no air in his lungs. As a toddler, Baker remembers being ineluctably drawn to water. Black Park Lake, near his home in Maidenhead, was a magnet. "Really, I feel it chose me," he says of his career and lifelong preoccupation. "Wherever there was water, if I wasn't paddling around the edges, I was jumping in off the sides. I gave my parents real problems."

 At 14 years of age, he and school friend Nick Mallabar, now owner/manager of the adventure-sports company System X, convinced their reluctant parents to allow them to embark on a maiden voyage to discover the source of the River Thames. Little did the parents know that on the way the pair would shoot every weir on the river. Over the next two years they completed a 200-mile trip down the River Wye to explore the Welsh coast, first in the double and then quickly graduating to high-performance slalom canoes. With no one to teach them, they researched paddling and survival techniques in books in the school library, perfecting the "Eskimo roll" (which enables a paddler to roll his capsized canoe upright) and other moves by throwing themselves down some of the river's formidable weirs.

"I look at some of them now and wonder how I made it," says Baker, "The Environment Agency has good reason for rules saying don't kayak down the weirs. I got away with it by the skin of my teeth. I'm sure that kind of thing couldn't happen now, but it was that relatively unregulated atmosphere that led to the way I am now."

At 16 years of age, the pair took a northbound train and over a period of a few months kayaked 700 miles south round the coast of Scotland, starting at Kingussie and ending at Hell's Mouth in north Wales. They paddled up to 12 hours a day and ran all the white-water rivers they found on the way. It was a life-threatening and life-changing experience.

"How I made it through my teenage years I don't know," Baker admits. "But that was the way I have always learned through life. I didn't really get on with supervision. I'm pretty well self-taught." That didn't prevent him from obtaining the formal qualifications needed to instruct. He holds advanced level "British Canoe Union Instructor and Examiner" status in all disciplines of the sport, including life saving, and still teaches kayaking occasionally at Brunel University.

"For a time I got hooked on wanting to pass on what I had learned to others," he says. There was even a brief spell at university, that is until the waterfall "bug" really began to bite. In 1986, in one of his first major waterfall challenges, Shaun and fellow kayaker Fred Wondre plunged over the previously unconquered Swallow Falls in north Wales.

 January 1987 saw him establish a new Guinness World Record for "free-fall waterfall kayaking" off of a 15m pure vertical drop at Sgwd-yr-Eira, in the Black Mountains of mid-Wales. News of his exploit was not well received by some of his peers. "I was pretty well slated by the press," Baker recalls. "They said all I was doing was throwing myself off and relying on gravity to get me to the bottom; that it was an unskilful discipline of the sport, likely to lead to my death."

The following year, when white-water freestyle competitions first came to Britain from the US, he decided that this was his opportunity to prove his paddling skills and silence his critics. Baker went on to largely dominate the sport over the next decade, winning the UK national title nine times, including the 1990 pre-World Championships, securing his last national championship in 1999.

 At 38 years of age, Baker is now a comparative veteran of his sport and an amazing survivor. Besides holding the world record for waterfall free-fall, he also holds Guinness World Records for speed altitude descents over drops of 75m and 50m, and also the land speed record for a kayak on snow. Of four early members of the Sector Watch NO LIMITS adventure-sports team, which he joined in 1992, he is the only one left alive.

Today Baker has retired from competition. "I've made my point," he declares. "I'm an out-and-out waterfall paddler. That's what I do. I don't feel I have any limits, that's the crux of it. There's a way down everything. If you threw enough empty kayaks over a waterfall, one of them would float free at the bottom and get away " even somewhere like Niagara. It's that one you want to be able to do." And what about the great Niagara Falls" "It's a long-term project," admits Baker. "It's just the most famous waterfall, although I'm not sure that that's the right reason to do it. But it has got some potential. There will always be a way down everything basically. I do turn my back on some waterfalls " but I'll never say never to them."