The Annamites: Vietnam’s Unknown Mountains

The Annamites don’t boast any towering snow-capped peaks. They don’t even feature the highest mountain in Vietnam; the “roof of Indochina” (3,147m Fansipan), sits much further north, near the Chinese border. But the Annamites remain a wild, underexplored range, perfect for those looking for a unique challenge.

The Annamites stretch 1,100km along the spine of Vietnam and Laos, dotted with dramatic limestone outcrops, 2,000m peaks and countless caves. Internationally, the area is best known by another name: The Ho Chi Minh Trail. The North Vietnamese Army used this complex web of paths to move fighters and supplies into southern Vietnam during the war. These hidden trails wove through dense rainforest and rugged passes, prompting the United States’ own National Security Agency to label it “one of the great achievements of military engineering of the 20th century.”

The United States did its best to relegate the achievement to a historical footnote. Planes dropped some two million tonnes of explosives on the trail between 1964 and 1973. The U.S. threw everything at the supply line: cluster munitions, defoliants, napalm. It even attempted cloud-seeding to extend the monsoon season. Despite this ferocious bombardment, the supply line remained unbroken, a testament both to the hardiness of those working the trail and to the unique topography of the Annamites themselves.

The Annamites, as shown in the wonderful illustrated children’s book Wonders of the Annamites. Photo: Eric Losh

Since the war, the range has slipped back into relative obscurity. Tourists visiting Vietnam take motorbike tours of the Ho Chi Minh Trail, but these barely touch the real routes. Instead, they take in key battlefields and strategic cities such as Huế and Đà Nẵng. The original trails and hideouts lurk in the region’s most inaccessible spots, including a handful of the highest peaks.

The highest mountain in the Annamites, 2,819m Phou Bia, lies on the edge of the range and was not part of the Ho Chi Minh Trail. Also the highest peak in Laos, it was used by guerrillas fighting for the other side of the conflict. Here, the CIA paid ethnic Hmong to counter North Vietnamese forces throughout the Annamites. Phou Bia is remote, covered with dense jungle, and officially off-limits due to military restrictions.

Hard travel through Vietnam’s jungle slopes. Photo: Martin Walsh

Phou Bia may be closed, but plenty more options exist for serious hiking. Unfortunately, exploration is complicated. There are obvious difficulties: monsoon rains, thick jungle and limited transportation. The more unusual difficulties include an unknown amount of unexploded ordnance from the war and thousands of wire traps for exotic animals, used both by local poachers and international wildlife crime syndicates.

One of my most nerve-wracking moments in Vietnam came deep into an eight-hour jungle hike when I stumbled across a fully camouflaged man, armed with a large, silenced assault rifle. I was armed with a rather less intimidating weapon, a telephoto lens. It occurred to me that we were probably both looking to shoot the same animals. Fortunately, he seemed as surprised as I by the encounter, and I slipped away without making small talk…

A crested serpent-eagle in flight. Photo: Martin Walsh

Whether the Annamites biodiversity can survive this rampant poaching remains to be seen, especially with so little available data and almost no government protection. But efforts are being made. The recent discovery of several new species may spur conservation efforts. The Vietnamese government has already made excellent progress with new forest reserves designed to protect habitat of one of these discoveries, the saola or so-called Asian Unicorn. One of the world’s rarest large mammals and one of the last discovered, the saola is endemic to the Annamites and can only be saved with significant investment.

Several national parks have recently formed on both sides of the range: Bạch Mã, Phong Nha Kẻ Bàng, Vũ Quang and Pù Mát in Vietnam and Dong Amphan and Nakai-Nam Theun in Laos. However, most of them are only theoretical tourist sites. Aside from Phong Nha Kẻ Bàng, they have extremely limited infrastructure and receive only a sprinkling of intrepid visitors a year.

The incredibly rare saola. Photo:

Phong Nha Kẻ Bàng is the exception, thanks to its astounding array of caves. This Kingdom of Caves became a UNESCO World Heritage Site in 2003 and features at least 300 caves, of which 30 are open to the public. The more accessible ones have become a huge draw; some three million tourists, including 50,000 foreigners, visited the park in 2015.

But the 900-square-kilometre park likely still hides some spectacular secrets. The jewel in Phong Nha Kẻ Bàng’s crown was only “discovered” by the international community in 2009. Quite how the largest cave in the world (by cross-section) remained hidden for so long is testament to the rugged, challenging landscape. A local boy, Hồ Khanh, first glimpsed the cave in 1991, but the roar of water and wind put villagers off from exploring its interior.

Years passed, and it was not until 2009 that Khanh, now an adult, was able to retrace his childhood steps and lead a Vietnamese-British team to the yawning chasm, now known as Hang Sơn Đoòng, that he had found nearly two decades earlier.

“The cave is very far out of the way. It’s totally covered in jungle, and you can’t see anything on Google Earth,” caver Adam Spillane explained afterwards. It was immediately apparent that Sơn Đoòng would be one of the largest caves in the world. The first expedition team made it over 3.5km into its vast system before a colossal 60m limestone wall, appropriately nicknamed the Great Wall of Vietnam, stopped them.

Sơn Đoòng cave. A person in the shaft of light provides scale. Photo: David A Knight

A return expedition the following year managed to get beyond this obstacle. The team reached the end of the cave passage and confirmed its gargantuan dimensions. All together, Sơn Đoòng measures more than four kilometres long, with a colossal middle passage 100m wide and 200m high. To put this into perspective, a Boeing 747 could comfortably fly through it, or if you prefer, you could throw in the Great Pyramid of Giza with 50m of space to spare. National Geographic described the discovery as “like finding a previously unknown Mount Everest underground.”

Incredibly, more underground systems have recently come to light. Just last week, the British Cave Research Association announced the discovery of 12 new caves in the province, an astonishing number given the wealth of surveys conducted in Phong Nha Kẻ Bàng in recent years. With so much still unknown within the Annamites’ most developed park, it’s hard not to get excited about what other discoveries, and adventure possibilities, await in this oft-overlooked mountain chain.