Since the remarkable commercial success of Michael Moore's Bowling for Columbine, the documentary as a cinematic form is undergoing a welcome renaissance, and are not just giving fiction-based features a run for their money, but beating them at their own game. Bowling Columbine had the political bite American features have lacked since the late 70s, Être et Avoir managed to present children in a moving and involving way without a hint of Hollywood mawkishness, and Rivers and Tides succeeded in getting closer to communicating what drives an artist than any based-on-fact drama. And now we have Touching the Void, a study of survival against insane odds that is more gripping, more thrilling than any other feature so far this year. Truth, as is often claimed, may not actually be stranger than fiction, but on the evidence of this extraordinary movie, it's a whole lot more exciting.

In May 1985, young British climbers Joe Simpson and Simon Yates decided that they were going to scale a treacherous unclimbed face of the Siula Grande mountain in the Peruvian Andes. Others had tried but had always been defeated by the sheer difficulty of the climb and the sometimes treacherous conditions, but the enthusiasm and youth of the two convinced them that they would succeed where others had failed. They elected to climb the mountain 'Alpine style', tethered to each other and carrying only enough food an equipment for a single shot at the climb, and with the weather initially on their side they made phenomenally good progress; even when the clouds built up and the wind and snow slowed them down to a crawl, they took shelter and battled on, and despite some intimidating snow formations on the mountain's ridge, they made it to the top. It was on the way down that the problems really began. The weather moved in again and they got lost, then Yates nearly fell, but they were a good way down the mountain when disaster struck - Simpson fell and broke his leg. As high as they still were and with the weather so poor, this meant only one thing - Yates would have to go on and leave Simpson, who was effectively a dead man. But Yates did not leave him, and devised a way of lowering Simpson 300 feet at a time using two ropes knotted together. Despite the excruciating pain this put Simpson through, it appeared to be working; that is until Simpson slipped over a ledge and was left dangling in mid air. Too weak and injured to pull himself up or communicate with Yates, who was dug into the snow, unable to lower the rope further and being slowly pulled towards the ledge and his own death. What happened next was to become part of mountaineering legend.

To suggest that mountaineers are a different breed to the rest of us is somewhat simplistic, but as someone whose stomach goes into knots if I get above the third floor of a building, the appeal of clambering up the side of a sheer rock or ice face with nothing below me but plummeting death has curiously managed to elude me. But I love mountains - I think they are among the most beautiful and awe-inspiring structures to be found anywhere in nature, and I have a genuine admiration for those who do choose to scale them. Hell, if I wasn't so terrified of heights, was younger and fitter and had the same sense of driven adventure, I'd certainly think about doing it too.

Mountaineering stories have a fascination for me in part because they often seem to involve individuals triumphing against impossible odds for no other reason than the thrill of doing it. But even within the ranks of great mountaineering survival stories, this one stands high. The above plot synopsis merely sets the scene - things get far, far worse before they get better. It is Simpson's struggle to survive, to get out of a seemingly impossible situation (and since he is the first person interviewed in the film, as well as the writer of the book on which the film is based, we know he does survive) that provides the meat of the film, gives it its narrative, and makes it such an extraordinarily compelling cinematic experience.

The structure is deceptively simple: interviews with the three main protagonists - Simpson, Yates and Richard Hawking, a non-climber who joined their team after meeting them en route and who stayed at base camp for the duration of the climb - alternate with reconstructions of the climb itself and subsequent descent. And that's it. So just what is it that makes it so extraordinary?

First up is the story itself. As anyone who has read Simpson's riveting book will tell you, this is one hell of a tale. Even told by a friend over a pint at the pub it would have you slack-jawed in astonishment, but told by those involved it is something else - all three interviewees here are engaging and hugely likeable, and are both honest and direct in the telling of their stories. Simpson in particular paints a most vivid picture of the suffering he went through - his description of what happened to the bones in his leg when it broke had the entire cinema audience during my first viewing of the film sucking air through clenched teeth in horror in a way that no staged version could match (the film's own recreation of the event is nicely matter-of-fact and doesn't even try and compete).

And then there are the reconstructions. Now I. for one, was more than a little cynical about this element, as reconstructions in documentaries are too often flatly performed and directed, but right from the early big close-ups of climbing tools being driven into ice and wider shots of the climbers dwarfed by the surroundings, there is a stamp of documentary authenticity on these sequences. This is enhanced further by unfussy performances by Brendan Mackey and Nicholas Aaron, playing Simpson and Yates respectively - even in the most emotionally charged moment, when Simpson, lying trapped in a crevice with no hope of escape, screams obscenities into the blackness, the performance never feels 'acted'. More often than not they are there to visualise the description of the commentators, but even at this level the film-making at the very least arresting, and at best is genuinely inspired. In particular the description of snow formations on the peak is intriguing, but actually seeing it is breathtaking. As the film progresses these scenes become less observational, less illustrative and more about connecting emotionally with Simpson's deteriorating mental state. Exhausted, chronically dehydrated, in constant pain and constantly convinced he was going to die, it is genuinely impossible to really imagine what Simpson went through, but director Kevin MacDonald (who won an Oscar in 2000 for his electrifying account of the 1992 Munich hostage incident) comes closer to visualising the experience than you'd expect from a docudrama, most vividly in his use of the snorricam so beloved of Darren Aronovsky, where the camera is connected directly to the actor so that it moves with him, creating a very disorientating effect in the viewer (seen in the front row of the cinema, it is particularly stomach-churning). It is also here that we hit the film's, and Simpson's own

The photography is often breathtaking, but never superficially so - the camera is used to most effectively create a sense of the sheer scale of the landscape and the task facing the two climbers, and later the seemingly impossible nature of Simpson's predicament. This is emphasised by the sound design, whether it be the crunch of snow beneath the climbers' feet, the genuinely heart-stopping sound of cracking ice when Simpson is crawling across it in pursuit of an escape route, or the infuriating running water that the desperately thirsty climber can hear but not reach.

Touching the Void pisses all over idiotic, overblown Hollywood fare like Cliffhanger and Vertical Limit from a mountainous height. This is the genuine article, a real climber in a real life or death situation, and a genuinely astonishing story of man's ability to survive against all odds. Abandon any negative preconceptions you may have of the documentary genre, formed by too many nights watching The History Channel - Touching the Void is more thrilling, more awe-inspiring, more genuinely, heart-clenchingly gripping than any fiction film I have seen all year.

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