A Crack in the Mountain: a breathtaking voyage into the world’s largest cave

In Il buco (2021), an exquisite meditation on the activities of the Piedmont Speleological Group, director Michelangelo Frammartino made Calabrian cave exploration feel a little like a mission to the moon. That analogy is echoed in Alastair Evans’s compelling new documentary A Crack in the Mountain, which focuses on the largest known natural cave on the planet: Hang Son Đoong in Phong Nha-Ke Bàng National Park, Vietnam. Among the contributors to Evans’s film is Bill Stone, CEO of Stone Aerospace, who describes how his childhood dream of becoming an astronaut shifted to a fascination with cave exploration – caves being, in Stone’s words, “the last terrestrial frontier”.

Evans’s film centres on the conflicts surrounding Son Đoong’s future, which has been contested since 2014, when plans were announced to build a cable car into the site. Such plans would dramatically increase visitor numbers but, dissenters argue, destroy the cave’s ecosystem.

At first it seems that A Crack in the Mountain will privilege white, Western perspectives such as Stone’s in this debate. The early sections of the film primarily comprise the reflections of members of the British expedition team that first surveyed and measured Son Đoong, as well as the visitors for whom the cave has become an integral and – at a $3,000 price tag – decidedly exclusive part of the Phong Nha tourist experience.

While the remarks of these contributors are engaging, the film grows in power when it widens its scope to include conflicting Vietnamese voices. Especially vital in this regard are the contributions of Lê Nguyen Thiên Huong, co-founder of the #SaveSonDoong movement, and author/activist Đang Hoàng Giang; both lay out the arguments for the cave’s protection from corporate exploitation, and describe the challenges of protesting in an oppressive one-party state. Contrasting with these critiques are the perspectives of the local porters for whom Son Đoong tourism provides a much-needed source of income.

Despite the emphasis on talking heads, Evans – the principal cinematographer as well as director, producer and editor – strives to make the film an arresting visual experience befitting the richness of the subject. Occasionally the aesthetic approach is overly fussy, especially when combined with a soaring score that’s too calculated in its efforts to create an atmosphere of mystical awe. But many shots are haunting, capturing the cave’s natural beauty in breathtakingly immersive images. Throughout, wider contexts are deftly sketched, but it’s the central conflict between environmental protection and economic opportunity that the film fleshes out with nuance and insight.

 ► A Crack in the Mountain arrives in UK cinemas 26 May.