Protecting Vietnam’s vast caves may have sparked a wildlife comeback

Thirty-five years ago, a Vietnamese hunter stumbled across the biggest cave on the planet — then promptly lost it.

Hồ Khanh was deep in the 400-million-year-old karst limestone landscape that straddles central Vietnam and Laos. Beneath Hồ’s feet lay wet cave systems that spanned hundreds of kilometers, but his focus was on the tangled jungle above. Here he hunted slow lorises, which he hawked as pets, and pangolins, whose scales are used in traditional medicine (and which perhaps helped spread COVID-19 from bats to humans). What he prized most, however, was agarwood, a rare, valuable and fragrant heartwood that could be carved into ornaments or burned as incense.

When a sudden storm broke, Hồ slipped into a cave for cover. The hammering rain blurred the world into noise, yet it couldn’t drown out the blustering chambers from the cave’s dark depths. When the skies cleared, Hồ resumed his hunt. With time, the memory of this small crack in the mountain dimmed, and Hồ returned to his primary income source: looting the jungle.

“Back then, we barely saw any wildlife,” recalls Howard Limbert, who began exploring the wilderness’s caves with his wife, Deb, in the 1990s. After several expeditions with the British Caving Association (BCA) in what became Phong Nha-Kẻ Bàng National Park in 2001, the Limberts were convinced that the region concealed vast, unknown caves. In 2007, when they heard Hồ’s story of a narrow opening that led to howling chambers, their curiosity was piqued. The three struck up a friendship, and Hồ renewed his quest to find what he’d lost. After a few failed missions, he finally guided the Limberts back to the cave the following year. No one had set foot inside for nearly 20 years.

Armed with equipment, Hồ and the Limberts were able to penetrate the cave. What they discovered defied belief.

The cave’s chambers were as wide as an airplane hangar and taller than the Great Pyramid of Giza. Two ceiling collapses had birthed flourishing subterranean jungles, home to great hornbills (Buceros bicornis) and particolored flying squirrels (Hylopetes alboniger). When the Limberts surveyed the cave, which Hồ christened Sơn Đoòng, it confirmed what they suspected: it contained the largest known cave chamber cross-section in the world.

The discovery of the world’s biggest cave (at least by one measure) drew global attention. International tourism took off, spearheaded by Vietnamese tour company Oxalis Adventure, which employed Hồ and the Limberts as consultants. By 2013, Oxalis was organizing multiday expeditions through Sơn Đoòng and various other caves in the vicinity. The media frenzy also prompted some controversial proposals: In 2014, a Vietnamese conglomerate suggested building a 10-kilometer-long (6-mile) cable car to bring mass tourism to the cave. Academics, conservationists, business leaders and environmental activists in Vietnam all voiced strong opposition, and the local authorities ultimately shelved the plans.

“When it comes to conservation, the national park has made significant progress,” says Tín Đoàn, a senior lecturer at Northumbria University in the U.K. and an advocate for sustainable tourism. Originally from the same Annamite mountain range as Phong Nha-Kẻ Bàng National Park — though around 300 km (190 mi) south — Đoàn studied tourism and sustainability in Australia and the U.S. before completing his Ph.D. in New Zealand. Throughout his time in academia, he’s kept a keen eye on the national park’s development.

“In terms of doing tourism, they have caves that appeal to different market segments,” he says. “It’s very strategic.” Sơn Đoòng hooks attention, but restricted numbers and a high price tag mean that most visitors check out the other caves in the area — like Hang Én, thought to be the world’s third-largest cave, and Paradise Cave, with raised wooden walkways suitable for less intrepid visitors and families.

The transformation of Phong Nha-Kẻ Bàng National Park’s visitor economy, Đoàn says, is a rare sustainable tourism success story. As strengthened conservation measures curbed illegal activity, hundreds of men from the area set aside their hunting gear for caving equipment, finding work as tour guides and porters. UNESCO put Phong Nha-Kẻ Bàng National Park on its World Heritage List in 2003, and by the time it expanded the area in 2015, illegal hunting and logging had fallen sharply. Structured, sustainable careers fostered by tourism replaced the lost jobs.

“There was no work,” remembers Phan Văn Thín, 37, who as a teenager made money from the jungle to pay for essentials like school uniforms and books. After graduating from university and a brief stint as a teacher, Thín joined Oxalis in 2011 as a tour guide and has since worked his way up to director of tour operations. “Now, most people work in hotels, restaurants or as guides. No one goes hunting or logging anymore.”

After 15 years of stringent conservation efforts, both Thín and Limbert say that wildlife populations are rebounding. “When we were surveying Sơn Đoòng, we rarely saw any primates,” Limbert says. “Now, we see big groups of Hatinh langurs [Trachypithecus hatinhensis] on nearly every trip.”

These charcoal-black monkeys with salt-and-pepper beards and messy mohawks were once hunted for their meat and purported medicinal properties. They’re endemic to Vietnam and Laos and are listed as endangered on the IUCN Red List. More elusive animals in the park include the saola (Pseudoryx nghetinhensis), an antelope-like bovine with straight sharp horns and a black-and-white patterned head. So rarely seen that it borders on legend, the saola is often referred to as the “Asian unicorn.”

National parks in Vietnam lack the resources to measure wildlife population numbers, but increased sightings of endemic species indicates a comeback, and Oxalis has begun incorporating this into some of its tours. In 2022, it launched the Hang Ba Deep Jungle Expedition, which visits six caves over four days in one of the most remote corners in the national park. Instead of looking for wildlife, Limbert says, visitors study animal tracks and look at photos taken by camera traps. “It’s more of an expedition than a tour, with a maximum of six tourists. We insist everyone is quiet, we ask them to wear darker clothing and we keep away from the animals.”

Though not opposed to Oxalis positioning wildlife as part of the appeal of their tours, Đoàn maintains the measured critical thinking of an academic. “It’s hard to know if it’s a good idea to include wildlife elements [in the tours] because we don’t know the full story … are these animals returning, or is it that the animals were always there and we weren’t aware?”

Đoàn also points to Laos, which he says has failed to make the same strides in combating poaching as Vietnam. Without good data, he says, how can we know that animals aren’t arriving in Vietnam after being driven away by hunters in Laos?

Limbert echoes Đoàn’s concerns for what’s happening on the Laotian side of the border, but remains optimistic for the future. In 2025, UNESCO expanded its recognition area again to include both Phong Nha-Kẻ Bàng National Park and Hin Nam No National Park in Laos, forming a transboundary natural World Heritage Site. Plans are already underway to increase conservation efforts in this remote part of Laos, and Limbert is mustering a team to help diffuse knowledge and experience across the border.

“I’m sure we will see the same kind of change as Vietnam,” Limbert says. “It’s happened in Phong Nha, and I’m sure it will happen in Laos too.”

By Joshua Zukas – Mongabay.com – November 13, 2025