Uncover the wonders of Hang Son Doong, the world’s largest cave

“Watch out for dinosaurs.”

I chuckle at our guide’s playful warning as I step into the vibrant jungle thriving inside Hang Son Doong, a 3-million-year-old cave nestled in central Vietnam. Water cascades from a massive crack in the ceiling, soaring over 100 meters (328 feet) above. A radiant sunbeam begins to descend along the jagged cliffs. The piercing calls of birds and macaque monkeys reverberate off the limestone walls, drifting in from the mysterious world beyond the skylight.

“Watch out for dinosaurs. That’s what we named this place when we first found it,” says caving expert Howard Limbert. The cave's ancient atmosphere made the comparison feel fitting.

We press on, venturing further into the vast expanse that some regard as the largest cave on Earth.

The discovery

Nestled in the heart of Vietnam’s Quang Binh province, within the UNESCO-listed Phong Nha-Ke Bang National Park, Hang Son Doong stands as one of Southeast Asia’s most awe-inspiring destinations.

Fewer people have ventured into the colossal chambers of this cave than have summited Mount Everest. Known as the Mountain River Cave, it was first discovered in 1990 by Ho Khanh, a local farmer seeking shelter from a passing storm in the jungle.

While there, he heard the roar of an underground river and saw clouds emerging from a large hole in the limestone. He reported his discovery to the British Caving Research Association (BCRA), who were based in Phong Nha at the time.

Unfortunately, Ho Khanh lost his way on his return, and the cave's precise location remained forgotten for 18 years. In 2008, while out hunting, he stumbled upon the entrance once more, returning the following year with Howard and Deb Limbert from the BCRA to explore it further.

They began their exploration of the cave, and by 2010, they confirmed it as the largest cave ever discovered based on the scale of its cross-section. The revelation sent shockwaves through the caving community.

The journey into Hang Son Doong

Stretching over five kilometers (three miles) in length and soaring to heights of 200 meters (650 feet), the main cavern of Hang Son Doong is so vast it could fit an entire block of New York City.

In 2013, Hang Son Doong was opened to the public for the first time, with the adventure tour company Oxalis offering the exclusive five-day expedition. By limiting the tours to a single operator, the cave has been protected from mass commercialization. Only 10 visitors are allowed per tour, with trips running once a week from February to August each year.

The ecosystem within Hang Son Doong is as extraordinary as its size, with its own localized weather patterns. Rare limestone cave pearls are scattered across dried pools, and the largest stalagmite ever discovered towers at 80 meters (262 feet).

The collapse of the cave’s ceilings has created openings known as dolines, allowing vegetation to flourish inside the cave. Microscopic life forms thrive in the cave’s eternal darkness.

Reaching Hang Son Doong is not for the faint of heart. The journey includes two days of rigorous jungle trekking and river crossings to get to the entrance, with nights spent camping in the cave or the nearby Hang En, the third-largest cave in the world. Inside, adventurers must abseil, climb, crawl, and swim through underground rivers to reach the cave’s farthest depths. It’s truly a one-of-a-kind adventure.

Despite the tough physical challenges, guests are well cared for. Each expedition includes two caving experts, three local guides, two chefs, two park rangers, and 20 porters. This extensive support team ensures the safety of everyone involved, while also safeguarding the cave's preservation with utmost care.

New discoveries

Beyond the unforgettable adventure and the cave's unique allure, the journey to Hang Son Doong has fostered a growing tourism industry, transforming the lives of many.

Quang Binh province, long one of the poorest areas in Vietnam, endured heavy bombing during the Vietnam War.

Unexploded ordnance still litters the fields and jungles, posing a daily danger to thousands of lives.

Many locals risk their lives by collecting and dismantling unexploded bombs to sell the dynamite and metal as scrap. While countless lives have been lost in this perilous endeavor, for many, it was the only way to provide for their families.

When the immense caves of Phong Nha were uncovered, travelers began flocking to the area for the first time. The local villagers embraced this new opportunity and turned their focus to tourism. The positive outcomes have led to a thriving local economy.

New community homestays are being built, breathing new life into what was once a poor town. The recent discovery of 57 additional caves has further stirred excitement among the people of Phong Nha, as their village quickly transforms into the adventure capital of Southeast Asia.

Driven by their passion, locals have established mountain biking, hiking, kayaking, and eco-tourism companies that complement the region’s caving offerings.

Fragile ecosystem

In recent years, a new threat has emerged that could jeopardize the integrity and environmental beauty of the region.

The Vietnamese development company Sun Group has been advocating for the construction of a cable car to Hang Son Doong, capable of transporting 1,000 visitors per hour. However, strong opposition from UNESCO and the activist group Save Son Doong led the Vietnamese government to temporarily suspend construction permits in 2015.

Some believe that this surge in tourism will continue to benefit the local community, while others fear it will bring irreversible harm to the ecosystem due to increased visitor traffic.

Similar cable car projects in Mount Fansipan, Vietnam's highest peak, and in Halong Bay have caused significant environmental damage. Will the world’s largest cave face the same fate?

The proposed cable car development still hangs in the balance, and it remains uncertain whether it will ever receive approval.

As one of the last untouched natural wonders in the area, Hang Son Doong is a truly extraordinary place that deserves to be safeguarded. We can only hope that a responsible, sustainable decision is made during these critical months ahead.

For now, the people of Phong Nha embrace the opportunities that the discovery of these vast caves has brought, while Hang Son Doong continues to stand as breathtakingly beautiful as ever.