Vietnam: Exploring The Largest Cave In The World

Deep inside Hung Ton Cave, a wooden ladder dropped iom down into darkness. As I stood alone at the bottom waiting for my fellow trekkers to descend, only the faint sound of muffled voices drifted from above. I scanned with my headtorch: the slate-grey of the cave wall was punctuated with bright dots, shining like diamonds; closer inspection revealed them to be the reflective eyes of huntsman spiders, each with leg spans as large as my outstretched hand. As I trained my beam on a particularly large specimen, the quiet of the cave was abruptly broken. Shouts of “Snake! Snake!” came from the top of the ladder. We had been promised an Indiana Jones-style adventure and, just 30 minutes into the first of the treks many caves, that promise was being delivered in spades.

Welcome to the world’s biggest cave – Hang Ton sits in the wider Tu Lan Cave area in Quang Binh province, a wild region of barely penetrable jungle-clad limestone karst that occupies Vietnam’s skinny waist-land, close to the border with Laos. The area is riddled with hundreds of deep caves, including one of the largest in the world – Hang Son Doong -which contains a cavern so tall that a skyscraper could fit inside it. A jungle also thrives in its vast interior, providing a habitat for monkeys and flying foxes. I’d been to the area before, and had met Howard and Deb Limbert, members of the British Cave Research Association. They were part of the team that first explored Son Doong, having been led to its mouth by local man, Mr Ho Khanh.

“When Mr Khanh spoke of the entrance to the cave, I knew we could be onto something extremely special,” Howard had told me. It was the mapping of Son Doong and its opening to tourists in 2013 that was the catalyst for the establishment of Vietnam’s newest adventure playground in the area around it. Howard is a former biomedical scientist who speaks in a soft, measured Yorkshire lilt; that is, until he gets onto his favourite subject: the caves. Then, he is in his element, and it’s near-impossible not to be swept along by his enthusiasm. “I’ve caved all over the world, but this place is special,” he said. “The people I work with here are real jungle folk – they are hard, hard men, but sociable and deeply honest.

Sitting around a campfire with these guys, singing and enjoying some rice wine in the evening, adds an extra layer to an expedition.” But while the massive Son Doong Cave has grabbed all the headlines and visitors, Howard, Deb and other British cavers have been busy scouting the area for alternative adventures: “I’m convinced there could be something even bigger here,” said Howard. “However, it’s not all about being the biggest – we’ve also found plenty of long, river caves for people to explore which we call the Tu Lan adventure. We’re talking about swimming through caverns full of fascinating formations and getting a real Indiana (ones feeling. You should try it.”

Eden on the edge – Those words were still fresh in my mind when, later that year, I travelled back to Phong Nha, the small town that is basecamp for the area’s trekking adventures, with a view to tackling Tun Lan myself. I checked in at the homestay owned by the discoverer of Son Doong’s entrance, Mr Ho Khanh. Not long ago, the road in front of his house was a rutted track peppered with old arms and ammo rusting in the scorching sun. Today it is smoothly paved, and his homestay business is growing. The money that the caves have brought to the town is evident. Nearby, the road crosses the Ho Chi Minh Highway West, which snakes close to the original Ho Chi Minh Trail – a key supply artery during the Vietnam War. We turned onto a side road bordered by glowing paddy fields as gaggles of school kids wearing bright-white cottons and carrying red plastic stools weaved their way around us.

Groups of farmers worked the land, their conical hats bobbing: the women hacked the crops with scythes while the men carried the bundles away. Once we were geared up with waterproof bags, lifejackets, headtorches and other supplies, we headed toward the caves. As we walked along a muddy farm track, our guide, Bamboo, pointed out the height of the last major flood in 2010. Looking around at the flat expanse between the hills, what Bamboo described was unfathomable. “The waters swelled to such a height that tall stilt-houses were totally submerged and countless cattle were killed,” he said. As a result, safe houses have now been built on higher ground and, in the nearby villages, numerous small huts perch on buoyant barrels, ready to be loaded with valuables should the waters rage again.

At the tail end of the dry season under a cerulean sky, the river still flowed strongly, meandering through buffalo-filled fields in the shadow of the vibrant-green hills. After a brief stop under the beating sun to photograph this Eden-like scene, we waded across the river and reached a rocky path that pitched skyward over a pass before descending into a hidden valley. “Illegal loggers set this path up before we came here,” Bamboo explained, pointing out the planks of wood they used to drag up timber. “They would use motorcycle-engine-powered winches to haul massive pieces of wood from the jungle.” Illegal logging and hunting for animals is still rife in the area, but the jobs provided through tourism are doing much to make the practice less of a necessity.

Going down – Before long we arrived at the mouth of the first cave: Hang Ton. Safety instructions were issued, then we cautiously stepped into the darkness. Grouped together at the bottom of a 6m-long ladder, a hush descended. In the daylight, conversation had flowed, but in the eerie darkness we stood quietly, training our torch beams on the glistening rock formations around us. As we approached the river that flows inside the cavern, the only sound was the drip-drip of droplets falling from stalactites onto the water’s surface.

Following Bamboo’s lead, we dropped our bags into the water and rolled onto our backs to swim slowly, slowly deeper into the cave. Bats swooped and dived, feeding on the thousands of tiny flies illuminated by the torch light. After a few hundred metres the sound of rushing water grew more intense as we reached the cave’s exit. The sense of discovery on emerging was even more palpable than that inside. Already in a remote part of Vietnam, we now found ourselves in what seemed like another world, emerging on a beach fronted by an impossibly pretty turquoise lake, which was fed by a waterfall thundering from the cave mouth.

The next cave we were to tackle was discovered by chance by a Dutch tourist named Kim. Also on the Tu Lan Trek, he’d sauntered off to find a quiet spot to relieve himself, away from the lagoon, and found what was subsequently christened Kim Cave. We swam through the chamber’s river to reach our campsite for the night: tents and hammocks had already been set up on the edge of an emerald-green lagoon. With time for one more adventure before supper, we swam across the water to Tu Lan Cave, after which the whole two-day adventure is named.

Inside, we ducked and weaved amid a labyrinth of stalactites, stalagmites and columns, sometimes having to pass backpacks through first in order to squeeze by. The cavern then opened up to reveal a bizarre set of shelves formed over thousands of years and containing almost perfectly round balls of calcium – cave pearls. Surrounding this, the walls were laced with a golden, glistening mineral and yet more shining eyes of innumerable huntsman spiders.

What else lies beneath? – Back at the campsite, we freshened up in the waterfall’s plunge pool as the sun sank swiftly behind the hills. Ravenous, we feasted on tender pork barbecued on spits over open flames accompanied by a local speciality dipping sauce of lime leaves, lime juice, garlic and chilli. With a glass or two of lethally strong rice wine, we kicked back to watch the stars. As we lazed, Bamboo pointed out two pairs of twinkling dots in the bushes – the eyes of flying foxes, quietly observing us from a distance. After a well-earned sleep – some of us in tents, others opting for swaying hammocks – we made our way into the massive arch of Ken Cave and lowered ourselves into its dark river waters.

Reaching the final stop of the two-day journey also involved its hardest swim, paddling 150m against the current. We re-grouped at the foot of a steep climb and ventured upward in single file before reaching a sheer drop-off. In front of us was a colossal column formed by the meeting of a stalactite and stalagmite. By now we’d seen tens of columns, but this one was in a league of its own. Photographs of what stood before us went viral a couple of years ago, so we had all seen it before, but we were still taken aback by its sheer scale and the surreal morphing of orange and cream hues on its richly textured surfaced.

The final cave tackled, we shed our lifejackets, helmets and headlamps and prepared for the trek back to base. For some, this proved the most challenging aspect of the trip, with the path climbing steeply through dense, primary forest in hot, steamy conditions. In places the thin, slippery trail snaked around vertiginous deep drop-offs – this was not a place where you wanted to put a foot wrong. After a couple of hours we found ourselves back at the river that we’d waded across the morning before, and over-heated members of the group collapsed gratefully into its cooling flow. Later, exhausted but content back at the Tu Lan base, we swiftly emptied its fridge of cold beers.

An uncertain future – That evening I went out for dinner with Chau A Nguyen, founder of Oxalis Adventure Tours, which runs the Tu Lan Trek. The day before, Chau and his team had been in the nearby city of Dong Hoi, anxiously waiting to hear whether the local authorities would allow tours of Son Doong to continue. When we met, the good news was writ large on his face. Chau spoke of his pride at helping develop the area from a tourist backwater – but he also voiced his fears for the future. There are now plans for a cable car project in the area, which would take people right to the mouth of Hang Son Doong. This would transform the town of Phong Nha as well as the UNESCO-listed cave area.

Tourist numbers would sky-rocket, and there are fears that the construction itself would have a devastating impact on the environment. On the flip-side, investors argue that cable cars have been built at sites of outstanding natural beauty before and that the project would inject much-needed capital into this relatively poor province. For now though, this is a region that remains pristine and ripe with the promise of adventure. And with Howard and Chau talking about the potential discovery of even more lengthy caves hidden deep in within these hills, who knows what adventures are still waiting to be revealed.