A guide to exploring Hang Son Doong, the largest cave in the world, located in Vietnam

Imagine waking up on a sandy beach next to a turquoise underground lake, illuminated by sunlight streaming through a massive skylight. Picture yourself standing in a natural cathedral formed by sinuous stone, sculpted over millions of years by erosion. Envision fording a subterranean river and being awestruck by the sight of mist and clouds inside this immense cave, so vast that it's hard to grasp its true size.

Every year, a fortunate few travelers to Vietnam get to experience this remarkable wonder. Hang Son Doong, or Mountain River Cave, was discovered in the lush forests of Phong Nha-Ke Bang National Park in 1990 by a local named Ho Khanh, who sought refuge from a storm. The cave remained hidden until 2009 when Khanh guided British explorer Howard Limbert and his team to map it for the first time.

Hang Son Doong is enormous. It’s so expansive that it can accommodate all the world's largest caves along with several 40-story skyscrapers. The cavern boasts a height of 503 meters (1,650 feet) and a width of 175 meters (574 feet), with a length of 9.4 kilometers (5.8 miles) winding beneath karst mountains. Remarkably, the cave is even larger than previously estimated; in 2019, British divers discovered a tunnel connecting it to another vast cavern, Hang Thung.

How can I visit Hang Son Doong?

Access to the world's largest cavern is limited to expensive guided tours, with strict caps on the number of visitors each year. However, if the cost or time commitment of a Hang Son Doong adventure isn't feasible, the nearby Phong Nha-Ke Bang National Park has plenty of other cave experiences to offer.

Spanning 1,233 square kilometers (476 square miles), this UNESCO World Heritage Site is home to some of Asia's oldest karst mountains, featuring remarkable cave systems that draw many visitors. Above-ground activities include fantastic jungle treks, journeys into scenic countryside, and historical sites related to the American War—definitely one of the highlights of any trip to Vietnam.

How do I go about booking a Hang Son Doong expedition?

Howard Limbert co-founded the adventure tour agency Oxalis in 2011, and in 2014, the company introduced multi-day exploration tours of Hang Son Doong. Participants camp in the stunning Hang En cave along the way, enjoying a swim in its underground lake before safely descending into Hang Son Doong with harnesses.

Over the course of two days, you'll traverse massive passages adorned with colossal rock formations, swim in hidden underground pools and streams, marvel at ancient forests thriving within the cave, and sleep at beautiful campsites beneath two dolines (giant sinkholes) that illuminate the cave with vibrant light. Wildlife encounters are frequent, including monkeys, flying foxes, snakes, bats, birds, and unique species of fish, shrimp, and insects adapted to total darkness.

Access to the cave is restricted to 1,000 visitors annually, resulting in high demand for spots. Each group of ten is guided by at least one of the British cavers who participated in the original Hang Son Doong expedition, and bookings for the caving season (January to late August) open up to two years in advance. Realistically, you should expect to join a tour approximately 18 months after your booking.

The four-day, three-night expedition is priced at US$3,000 per person (with US$620 allocated for the maintenance of Phong Nha-Ke Bang National Park). This fee covers pick-up and drop-off in the city of Dong Hoi (the nearest town with an airport), along with the services of a cave expert, tour guide, safety assistants, cooks, porters, food and drinks, tent accommodations, and all necessary safety gear. However, comprehensive travel insurance is required.

Are there other caves in Phong Nha-Ke Bang National Park that are worth a visit? 

If you can't take part in a Hang Son Doong expedition, consider an overnight trek with Oxalis to Hang En, another of the world's largest caves. You'll set up camp on a sandy beach next to a shimmering pool within the cave and hike through ancient jungle to reach it.

Oxalis also conducts expeditions to the Tu Lan cave complex. You can choose from overnight camping trips or longer multi-day adventures that include rappelling into underground rivers, exploring Hang Tien, technical training in the cave's darkest areas, and interactions with the Nguon people in a secluded mountain village.

Oxalis offers a multi-day Hang Ba Deep Jungle Expedition, where you'll trek through primary forests in search of wildlife such as gibbons, wildcats, langurs, and wild boars, while also exploring six recently opened caves that are now accessible for guided tours.

Another tour operator is Jungle Boss, offering a range of overnight and multi-day adventures, including a three-day journey through Hang Thung, the massive cave connected to Hang Son Doong. Highlights feature rappelling and camping beside the Ma Da subterranean lake. There's also an overnight excursion to Hang Pygmy, the world’s fourth largest cave, which includes paddleboarding on yet another breathtaking underground lake.

What if I can’t spare time for an overnight adventure?

Pressed for time? From the village of Son Trach, you can take a day trip to Hang Tien, the largest dry cave in the Tu Lan system, where stunning calcite formations and rimstone pools await. Alternatively, you can zipline 400m (1312ft) above Hang Toi (Dark Cave) and squish through thigh-deep mud in total darkness before enjoying a kayaking session and a swim.

A visit to Phong Nha Cave involves a relaxing boat ride from Son Trach, passing picturesque rice paddies and limestone peaks as your vessel silently glides by magnificent illuminated stalactites and stalagmites. Climbing the 330 steps to Tien Son Cave reveals 9th-century inscriptions from the Cham era.

Even if caves aren’t usually your thing, Paradise Cave might just change your perspective. Electric buggies transport visitors to this stunning cavern surrounded by lush karst peaks. The entrance may be small, but inside lies a breathtakingly massive cavern adorned with surreal rock formations. Both Phong Nha Cave and Paradise Cave can get crowded with tour groups, so early morning visits are recommended.

What factors should I consider when selecting a tour operator?

Phong Nha-Ke Bang National Park is littered with unexploded ordnance from the American War, and many regions are accessible only on foot with a licensed tour operator. While Paradise Cave and Phong Nha Cave can be visited on day trips, seeing Hang Son Doong, Tu Lan, Hang En, and other caves requires joining an overnight trek with a licensed guide.

Oxalis is the sole operator for Hang Son Doong caving tours and also conducts multi-day jungle expeditions to Hang Ba. Meanwhile, Jungle Boss holds exclusive rights for overnight treks to Hang Pygmy and three-day, two-night explorations of Tiger Cave. They also provide multi-day jungle treks and rappelling adventures to the base of Do Quyen waterfall. Ecofoot, led by the knowledgeable jungle guide and conservationist Hai, organizes visits to the park's Wildlife Rescue Centre and offers both daytime and nighttime jungle treks.

When selecting a tour operator, inquire about group sizes and the guide-to-client ratio, and clarify what is included in the package price. Many accommodations in Son Trach or Dong Hoi can arrange jungle treks in Phong Nha-Ke Bang National Park with independent local guides, but the quality may vary, so it's advisable to seek recommendations from fellow travelers.

What is the best time to go caving in Phong Nha-Ke Bang?

Similar to other regions in Vietnam, the ideal time to visit depends on your activities and interests. Winters (December to March) can be chilly, featuring a balance of sunny and rainy days, but Hang Son Doong boasts its own microclimate, making January and February the prime months to observe sunbeams illuminating the depths of the cave.

In late January or early February, Vietnam celebrates the Tet festival, making it the peak travel season. Residents of Phong Nga enjoy lively festivities, sometimes using unexploded ordnance as makeshift fireworks and sharing rice wine with those passing by.

From April to May, the national park showcases its beauty; the weather warms up, the scenery becomes lush, and wildflowers bloom abundantly. You might also see clouds and mist forming within Hang Son Doong.

Summer (June to August) brings the hottest and most humid conditions, but the trekking paths to Hang Son Doong and other caves are shaded by trees. Inside Hang Son Doong, temperatures range from a pleasant 22–25°C (72–77°F), making it ideal for swimming in the streams and underground lakes. Autumn (September to November) introduces tropical storms and heavy rainfall, causing floods in the jungle and river caves, so caving trips are limited to January through late August.

How long should I plan to stay here?

If you're embarking on a Hang Son Doong expedition, allocate six days for the adventure. However, if you prefer a more casual exploration of the caves and the scenic attractions in Phong Nha-Ke Bang, four to five days is sufficient. Consider an overnight trek to Hang En or the Tu Lan cave system, followed by a day biking through the beautiful Bong Lai Valley, and then take day trips to Phong Nha Cave and Paradise Cave. Alternatively, you could mix an overnight trip to Hang Pygmy with day visits to Hang Tien, Hang Toi, and Bong Lai Valley.

Is it convenient to get around Phong Nha-Ke Bang National Park? 

Phong Nha-Ke Bang National Park extends westward to the Vietnam-Laos border, with Son Trach (also known as Phong Nha Village) at its heart. This village serves as a major stop for open-tour sleeper buses coming from Hanoi and Hoi An. Dong Hoi, located 50km southeast of Son Trach, is the closest city with a domestic airport, while Danang and Hanoi host the nearest international airports.

Dong Hoi also features on the train line connecting Hanoi and Ho Chi Minh City, with regular public buses linking it to Son Trach. Many accommodations in Son Trach offer both private and shared car transfers to and from Dong Hoi, and motorcycle transfer services are available from Hanoi, Hue, and Hoi An.

To explore the more accessible areas of Phong Nha-Ke Bang National Park, it's best to have your own transport. Cycling or riding a scooter is a delightful way to navigate the rural roads around the park; rentals are available from guesthouses, homestays, and hotels in Son Trach, where staff can often provide maps.River taxis offer connections between Son Trach and the stunning, untouched Bon Lai Valley, allowing you to bring bicycles and motorbikes aboard.

The road conditions within the park can be inconsistent, and routes aren't always clearly marked, but you can find route information on the independent site Vietnam Coracle. Consider joining a motorcycling tour with Thang Phong Nha Rider, where an enthusiastic local team will guide you to the park's highlights. They also offer motorcycle transfers to farther destinations like Hue or Khe Sanh.

Commonly asked questions

Is prior caving experience required?

Prior caving experience isn't needed; the expedition agency will handle all the details.

What equipment should I pack?

Key items include quick-drying, long-sleeved shirts and trekking pants, breathable shoes with good traction (avoid waterproof/Gore-Tex boots), warm layers for colder months, and swimwear, shorts, and T-shirts for summer. Don't forget essentials like mosquito repellent, sunscreen, antifungal cream, environmentally friendly personal hygiene products, a dry bag, and power banks for your devices.

What level of physical fitness is required?

Some trekking experience is crucial. In the year leading up to your Hang Son Doong expedition, try to complete at least one overnight trek and one or two day hikes of at least 8km that include steep, mountainous terrain. Regular exercise is important to keep a good fitness level, as the expedition entails trekking on rocky paths, some steep ascents, abseiling inside the cave, crossing rivers, and climbing over large boulders.

Are there age limits for caving adventures?

Most multi-day caving and jungle treks accept participants aged 16 (or 18) to 70. However, Oxalis also provides day-long introductions to the Tu Lan cave for children aged 6 and older.

What are the accommodations like?

During overnight cave expeditions and jungle treks, you'll sleep in tents, with meals and drinks provided by the operator. Porters carry camping gear to the campsites. Many cave expeditions set up camp on sandy beaches alongside underground rivers and lakes, offering chances for swimming.

What are the bathroom facilities like?

Campsites within the caves feature eco-friendly composting toilets. While there are no showers, you can wash off in the rivers and lakes inside the cave. Avoid using shampoo or soap to prevent water contamination; for some campsites, dry shampoo and wet wipes are recommended.

Should I carry cash on the trek?

While there are limited opportunities to spend money during your trek, the infrastructure in Son Trach, the nearest village to the caves, is sparse. There is one ATM, which may not always be functional, so ensure you bring enough cash for your expenses before and after the expedition.

Is tipping expected?

Though tipping isn't a strong tradition in Vietnam, it is always welcomed. A typical tip for tour guides ranges from VND 100,000 to 200,000 per day, with less for porters and cooks, depending on the tour's length and difficulty. It's best to tip in the local currency, using small denomination notes when possible.