Free Solo

Free Solo has been heavily pushed for Best Documentary this year. Though very good, it's unlikely to make it to the top. But it is by far the scariest.

There's something about watching a feature film that involves real stunt work instead of CGI that's much more gripping. Even if you haven't heard reports of anyone getting killed or injured on set, you'll be on the edge of your seat because of the danger involved. Free Solo is the documentary equivalent. It follows ambitious young climber Alex Honnold as he tries to become the first person to climb the 3,000ft high El Capitan Wall in Yosemite all by himself, without safety equipment.

Co-directors Jimmy Chin and Elizabeth Chai Vasarhelyi, know for their work on Meru, are both experienced mountaineers themselves, and it's partly their trepidation that gives the film its intensity. We don't spend all of it on the climb itself, however. Alex isn't daft - he spends a lot of time going up and down the Wall on ropes first, working out how to manage the difficult bits. He works on getting himself into the right place psychologically. And the documentarians spend time getting to know him, familiarising themselves (and the audience) with his day to day life. We learn about his family background, see him engaged in public speaking and attend a visit to a doctor who informs him that there's something different about his brain - essentially, it takes an unusual degree of stimulus to make him feel fear. We also see him tentatively embarking on a new relationship, with a young woman whom he has to send away when embarking on the climb itself because he's too distracted by her fear.

At this stage you may be observing this unlikely character and asking yourself what's his motivation? I mean, why climb up a towering rock face without ropes when you could perfectly well do it with them? Even some of those who love the challenge and thrill of climbing think this is crazy. Chin and Vasarhelyi don't try to explain - it's not clear that they can get their heads around it either. But we see it. We see it in Alex's joy on overcoming each obstacle, in the compulsive way he works towards the climb, in his excitement when talking about previous ascents. It seems to hinge on successfully testing what he's capable of all by himself, both physically and psychologically. There's a sense that he's exploring the way he fits into the universe.

The final stretch, when Alex commences the climb, is some of the most nail-biting cinema you will ever see. The film crew have next to no warning. They aim to capture the experience as best they can but don't want to get anything in his line of sight. What they achieve with zoom lenses and a careful choice of angles is very impressive, but of course it's the climb itself that holds the attention - the swings, the jumps across sheer rock, the knowledge that one millisecond of lapsed attention, one misplaced fingertip could be fatal. You won't be able to take your eyes away.

Watch this film on the biggest screen you can. And don't try what Alex does at home.