A gripping documentary about climber Alex Honnold and his attempt to climb El Capitan without ropes or safety gear.

You’ll need a cool head for heights, too, to watch his dizzying feat of scaling the almost sheer 3,000ft rock face in California’s Yosemite National Park.

Even the coolest of cool heads will find their palms sweating and hearts racing as they watch Honnold’s solo ascent, filmed by co-directors Jimmy Chin and Elizabeth Chai Vasarhelyi and their team of skilled climber-photographers.

Honnold’s climb is truly mind-boggling. As fellow climber Tommy Caldwell puts it, ‘Imagine an Olympic gold medal-level achievement where if you don’t get that gold medal, you’re going to die.’ Who would attempt something like that?

Charting Honnold’s intense preparations for the attempt on El Cap over several years, the directors go some way to answering this, portraying a supreme athlete with laser focus and a jaw-dropping attitude to risk. In the course of filming, Honnold undergoes an MRI scan, which reveals that his amygdala, the part of the brain responsible for fear, needs a much higher level of stimulation than the average person’s.

He also acquires a girlfriend, Sanni McCandless, which introduces another level of suspense. Will the relationship affect his concentration? How will Sanni cope with the emotional vertigo?

We can only hang on in there and marvel.