A Crack in the Mountain review — eye-opening documentary about an epic cave system

Much of what you see in A Crack in the Mountain is insanely beautiful. Therein lies the problem. The subject of this compelling documentary is Hang Son Doong in central Vietnam: not just the world’s largest cave passage, but beyond spectacular even witnessed secondhand. Director Alastair Evans duly captures cave ceilings whose vaulted grandeur recalls cathedrals but have the height of skyscrapers; leviathan waterfalls and rainforests; celestial light and sudden pools of ink-spot darkness. One explorer says the cave is like living cinema; another like nothing on Earth. 

But Evans also tells a story: one of the faultline between conservation and economics. Hang Son Doong was only discovered by a Vietnamese farmer in 1990. For most of the three decades since, it has remained a relative secret, and pristine as a result. The looming question: how much longer?

Though the vista remains the heart of the film, the lens also widens. A principal is Huong Nguyen Thien Le, a childhood reader of Jules Verne who later fell in love with her own country’s journey to the centre of the Earth. Now, she campaigns to limit the number of tourists tramping through it. The case for that is obvious. You too will blanch when a mooted cable car threatens to raise the human presence from a few hundred people daily to a thousand an hour.

Yet the film has integrity enough to deal head-on with competing realities. When Hang Son Doong was stumbled on, we learn, not a single manmade structure stood for miles around. The area had been bombed into a crater in the war with America, and simply never rebuilt.

Now the shadow of mass tourism offers local people a possible escape from poverty. Jobs as porters are already cherished; more would come with hotels and restaurants. Whose place is this paradise anyway? And whose place to decide the future? Evans lets us sit with those troubling, unresolved questions, at the same time as we marvel at the natural magic under Vietnam.

★★★★☆

In UK cinemas from May 26