Son Doong Cave — Inside the World's Biggest Cave (2026-2027)

What is Son Doong Cave?

For people learning about Phong Nha, Son Doong Cave is usually the first name that appears. Search results sometimes label it as "Son Doong Cave Vietnam", and a surprising number of people also search "song doom cave" when they mean Hang Son Doong. Same cave, different spelling mistake. It is the biggest cave in the world by volume and one of the most famous natural sites in Vietnam. The cave sits in the core area of Phong Nha - Ke Bang National Park, in Thuong Trach Commune, Quang Tri Province, Central Vietnam. Many older maps and travel pages still write Quang Binh Province, because that was the former province name.

Hang Son Doong was found by Ho Khanh, a Phong Nha jungle man, in 1990. He did not enter deeply at that time. The cave had strong cold wind, fog at the entrance and the sound of a river inside, so he returned and later forgot the exact route. In 2009, he guided the British - Vietnam Cave Expedition Team, led by Howard Limbert, back to the entrance. The team surveyed and measured the cave, then announced Son Doong as the largest natural cave in the world.

The measured volume of Son Doong is 38.5 million m3. The main passage is nearly 9km long, with some sections over 200m high and more than 150m wide. This is why guides and cave experts often explain the size by using simple examples: a 40-storey building could fit inside some parts, and a Boeing 747 could fly through the largest passage without touching both walls.

Please note the difference between Son Doong and Mammoth Cave. Mammoth Cave in Kentucky, USA, is the world's longest known cave system. Son Doong is the world's largest natural cave by volume, with a very large single cave passage. In simple search language, it is the biggest cave in the world, not the longest cave system. The measurements were accepted by senior karst geologists, including Dr Tony Waltham, and Guinness World Records recorded Son Doong Cave as the world's largest natural cave in 2013.

Inside Son Doong, you will not see only a big empty tunnel. The expedition route has an underground river, giant stalagmites, fossil passages, cave pearls, two dolines where sunlight comes into the cave, and a forest growing under the collapsed roof. This is the reason many people describe Son Doong as an underground world rather than just a cave.

If you are curious you can find out the deepest caves in the world in our guide!

Origin of the name Son Doong

In Vietnam, the person who finds a cave normally takes part in naming it. After the 2009 survey, Ho Khanh and the cave experts discussed the name and decided to call it Son Doong.

Son means mountain. Doong is the name of the valley where the Bru-Van Kieu ethnic minority people live and where Thuong River comes from. The name can also be understood as the cave in the limestone mountain with an underground river flowing through it. For Son Doong, this meaning is quite suitable, because the underground river is one of the main features of the cave.

Unique features of Son Doong Cave

Son Doong has a total length of nearly 9km and a volume of 38.5 million m3. Before Son Doong was explored, Deer Cave in Malaysia was often mentioned as the largest natural cave, with about 9.5 million m3. Son Doong is around five times larger by volume.

However, people do not come to Son Doong only to hear the numbers. You go inside this cave to see a river, mist, sunbeams, forests, fossil walls, giant formations and campsites set up deep under the mountains. Below are the main places on the Son Doong expedition route.

Hope and Vision Passage

Explorers using their headlamps to light up the massive Hope and Vision chamber inside Son Doong Cave

Hope and Vision Passage is one of the largest sections inside Son Doong. From the beginning of this passage, you can see the light from Doline 1, about 1.5km away. The light is still inside the same cave passage, so it gives a clear feeling of the size.

Cave experts estimate that a 40-storey skyscraper can fit in this passage. It is also large enough for the Boeing 747 comparison. The world's tallest known stalagmite, about 80m high, is here. The Hand of Dog formation, about 60m high, is also in this area.

Underground river

There is an underground river running through Hang Son Doong Cave. The water comes from Hang En Cave and Khe Ry Cave, with Khe Ry taking water from near the Vietnam - Laos border area. From the Son Doong entrance, you have to cross knee-deep rivers twice before reaching Hope and Vision Passage. There are emergency bridges when the water level is high.

Along the river, small waterfalls create loud rumbles through the passage. Sometimes the cave is filled with mist, especially on humid days. When the group moves with headlamps, the light can cut through the mist and make the cave look very different from the usual dark limestone passage.

The underground river disappears near Doline 1, about 4.5km from the cave entrance. In 2019, Howard Limbert and cave diving experts Martin Holroyd, Rick Stanton, Jason Mallinson and Chris Jewell carried out a dive exploration here. They reached 78m depth, and the passage was measured about 93m overall, but they could not continue with normal air cylinders. If Son Doong is connected with Thoong Cave, about 600m away, its known volume may increase by about 1.6 million m3.

Tourists paddling small boats with bright blue underwater lights along a dark river inside Son Doong Cave

Doline 1 - Watch Out For Dinosaurs

The collapsed ceiling of Son Doong formed a large opening to the outside, called Doline 1 or skylight. It is about 450m from the top opening to the cave floor. This is also where the underground river disappears into the flooded passage below.

From January to March, on sunny days, giant sunbeams can come into the cave from about 11am to 1pm. The sunbeam, the mist from the river and the dark passage create one of the most famous views in Son Doong. Google used this moment for a Google Doodle on April 14, 2022.

The expedition team named this area Watch Out For Dinosaurs because the ferns, fog and high limestone cliffs look like a prehistoric scene. Many visitors remember this place clearly, because it is the first time the cave opens to the sky in such a dramatic way.

Doline 2 - Garden of Edam

About 1km from Doline 1, you reach Doline 2, also called the Garden of Edam. This doline has a forest growing about 200m deep inside the cave. With a large opening above, sunlight enters and allows ferns, begonias, vines, shrubs and trees to grow along the route.

Biologists have recorded more than 200 plant species in Son Doong, including moss, algae and trees up to about 30m high. You have to trek for about 30 minutes through this underground forest to reach the second campsite. The feeling is unusual because you come out from a dark cave passage, walk through a green forest, and then return into darkness again.

Fossil passage

The fossil passage is next to the underground river, about 40m below the campsite near Doline 1. The walls have fossilised corals from an ancient seabed, hundreds of millions of years old, from the time when the limestone was still forming.

There is also an underground lake here, with water around 17 to 20 degrees Celsius. Depending on water conditions and guide instruction, visitors can swim here after a long trekking day. Life jackets and headlamps are required for safety.

Cave pearls

Cave pearls are formed when water drips from the ceiling and carries calcium carbonate into gour pools on the cave floor. In Son Doong, they come in different sizes, from small like peas to larger pieces like baseballs.

The pearls look clear under headlamps, especially when fresh water is running through the pools. These cave pearls are only ordinary calcium carbonate deposits. They have no commercial value, and if they are taken outside, they dry quickly and become plain. They must stay inside the cave.

Passchendaele Passage

Passchendaele Passage is a 600m section below the Great Wall of Vietnam. When the expedition team first came here, the water had drained away and left a hip-deep muddy passage. Crossing it took a lot of effort.

The mud reminded the team of the Battle of Passchendaele in World War I, so they used that name. In other months, or after heavy rain, water fills the passage and forms a jade-green underground lake. When the lake is full, visitors may cross by raft or boat.

The Great Wall of Vietnam

In April 2009, after nearly 10 days of exploration, the team reached a giant calcite wall about 90m high. It blocked the way forward. Because they did not have enough specialised climbing equipment, they returned.

No one knew what was behind the wall at that time, so the team called it the Great Wall of Vietnam. In March 2010, Howard Limbert and the team came back with climbing gear and a National Geographic film crew. They climbed over the wall, walked about 400m more and found the exit, completing the full survey of Son Doong.

Today, the Great Wall of Vietnam is part of the official expedition route. Guests climb it with harness, lifeline system and support from the safety team.

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Discovery and exploration

The story of Son Doong started with Ho Khanh, a local man born and raised in Phong Nha. Since he was young, he spent many days in the jungle as a lumberjack and also searched for agarwood and forest products. At that time, many local families still depended on the forest for income.

In late 1990, during one jungle trip, Ho Khanh met a storm and looked for shelter. He found a small cave entrance below a cliff. When he came close to the entrance, he saw mist blowing out and heard the sound of a roaring river inside.

He felt strong cold wind from the cave, but he did not go farther. He was alone and the weather was bad. Later, he thought the cave was similar to many others in the jungle and did not remember the exact location.

In 2007, Howard Limbert and Deb Limbert from the British - Vietnam Cave Expedition Team came to Phong Nha for cave research. Based on limestone topography, river systems and fault lines, Howard believed that there must be a very large cave somewhere after Hang En, but the entrance was unknown.

During a conversation, Ho Khanh mentioned the cave he had seen years before, with strong wind, fog and the loud sound of water. Howard and Deb were interested and asked him to try to find it again.

Ho Khanh searched many times. In 2008, during another trip into the forest, he found the entrance again. This time he memorised the route carefully by using mountains, trees and jungle marks. After returning to Phong Nha, he contacted the expedition team.

On April 7, 2009, Ho Khanh led the British - Vietnam Cave Expedition Team to the entrance. Peter MacNab was the first team member to step inside Son Doong Cave. It was also the first time Ho Khanh entered the cave he had found 19 years earlier.

Son Doong Cave survey timeline

• Late 1990: Ho Khanh discovered the cave entrance during a jungle trip.

• 2008: Ho Khanh found the entrance again and remembered the route.

• April 07, 2009: Ho Khanh guided the British - Vietnam Cave Expedition Team led by Howard Limbert to survey Son Doong. Peter MacNab was the first person from the team to enter.

• April 14, 2009: The cave was named Son Doong and announced as the largest natural cave in the world.

• March 17, 2010: The team climbed the Great Wall of Vietnam, reached the exit and completed the survey. Son Doong was measured at nearly 9km long and 38.5 million m3 in volume.

• 2013: Guinness World Records recorded Son Doong as the world's largest natural cave.

• March 31, 2019: Cave divers explored the underground river, reached 78m depth and found a passage measured at about 93m overall, but did not reach the end.

Surveys of Son Doong Cave

The first survey in April 2009 did not finish the cave completely. At the far end, the team found the large flowstone wall blocking the way. A small light could be seen high above, but without technical climbing equipment it was not safe to continue, so the team returned with the measurements they already had.

In March 2010, the expedition team returned with climbing gear. National Geographic TV also joined to film the cave and the climb over the calcite wall. After passing the Great Wall of Vietnam, the team walked about 400m more and found the exit. From this point, the full length and volume of Son Doong were confirmed.

The 2019 dive survey focused on the underground river near Doline 1. Cave experts believe this flooded passage may connect with Thoong Cave, around 600m away. The diving team found a deep underwater passage but could not explore farther with normal equipment. If this connection is proved later, the known volume of Son Doong may increase by around 1.6 million m3.

Geology and formation of Son Doong

Son Doong is located in the oldest and largest limestone massif in Southeast Asia. The limestone is more than 400 million years old. Long ago, this area was under the sea. Limestone was formed from coral, shells and other marine organisms, together with chemical calcium carbonate deposits.

Later, movements of the earth's crust lifted these sediment layers and formed the limestone mountains. According to geologists, Son Doong formed about 2 to 3 million years ago along a fault line of the Truong Son Range.

Rainwater and river water become weakly acidic when they contain dissolved carbon dioxide. Over millions of years, this water dissolved limestone, widened cracks and created large underground passages. Heavy tropical rainfall and thick limestone beds helped Son Doong grow to a very large size.

At some places the cave ceiling became too thin and collapsed. These collapses created the dolines that allow sunlight to enter Son Doong today. The Thuong River still flows through the cave, so the formation process continues.

Ecosystem inside Son Doong Cave

Because Son Doong is very large, it has its own weather system. Differences between the air inside the cave and outside air create airflow through the passage. Mist from the underground river can collect inside the cave and sometimes looks like clouds in the darkness.

The temperature inside Son Doong is cooler than outside. In summer it is usually around 22 to 25 degrees Celsius, and in winter about 15 to 20 degrees Celsius. During hot months, the cave can be 8 to 12 degrees cooler than the jungle above.

At the dolines, where sunlight enters, plants can grow. More than 200 plant species have been recorded inside Son Doong, including moss, algae, vines, shrubs, ferns and trees up to about 30m high. Monkeys, hornbills, flying squirrels and bats have also been recorded around the forest areas.

In the dark parts of the cave, scientists have found more than 7 new animal species, including cavefish, woodlice, millipedes, spiders and scorpions. These cave animals have adapted to darkness, so many have white or transparent bodies and no working eyes.

To protect the cave, the expedition follows strict conservation rules. Visitors cannot touch formations. All waste, including human waste, is carried out. The annual number of visitors is limited to around 1,000 people.

Son Doong expedition tour

Duration and group size

The Son Doong Expedition is now operated as a 4-day, 3-night adventure tour. In the past it was longer, but the current program still includes jungle trekking, river crossings, camping inside the cave, safety sections with harnesses and the climb up the Great Wall of Vietnam.

Each group has a maximum of about 10 guests. A support team of about 30 people joins the expedition, including guides, safety assistants, porters, cooks and national park rangers. The support team carries equipment, prepares campsites, cooks meals and helps manage safety.

The tour normally operates from January to August. Son Doong is closed from September to December because rainy season water levels can make the route unsafe.

Son Doong tour price

The Son Doong Expedition costs about USD 3,000 per person. The price includes guides, safety equipment, camping gear, food, drinking water, national park permits and transport from Dong Hoi. Visitors prepare their own suitable clothes, trekking shoes and personal items.

The price is higher than standard cave tours because of the large support team, remote location, safety requirements and conservation rules.

Fitness requirements

Son Doong is a difficult expedition and is normally rated at the highest level. It is an adventure expedition, not an easy sightseeing cave.

The route includes about 25km of trekking and caving over 4 days. There are jungle trails, river crossings, rocky terrain, boulder scrambling and the 90m rope-assisted climb up the Great Wall of Vietnam. Guests also carry a personal day pack.

Applicants usually must be from 18 to 70 years old and need to complete health and fitness information before being accepted. Recent trekking experience is required, including at least one overnight trek and day hikes of 8km or more with elevation gain.

Training is recommended before the trip. Hiking with a backpack, climbing stairs, running and walking on uneven terrain are useful preparations for the route.

Booking Son Doong Cave

Son Doong is difficult to book because the number of guests is strictly limited. As of the latest official tour information, the 2027 expedition is fully booked and 2028 has limited availability.

Independent access is not allowed. Son Doong is inside the protected core zone of Phong Nha - Ke Bang National Park, so visitors must join the authorized expedition. There are no normal day tickets and no alternative operators for Son Doong.

Camping inside Son Doong

Campsites inside Son Doong are prepared by the porter team before guests arrive. Tents, cooking areas and composting toilets are set up at the campsite. Meals are cooked by the expedition team.

There is no mobile phone signal and no wifi inside the cave. Staff carry satellite phones for emergency use. Visitors should inform family or travel contacts before departure, because communication is not available during the expedition.

Before booking Son Doong

Son Doong booking notes:

• Gear check in Phong Nha first. Do not wait until the morning of departure.

• Shoes: used trekking shoes, not new shoes. Good grip. Quick drying if possible.

• Socks: bring extra pairs. Wet socks are common after river crossings.

• Clothes: quick dry shirt, long trousers, one light warm layer for cave camp.

• Hands: thin gloves help on sharp limestone and rope sections.

• Dry bag: medicine, phone, camera battery, passport copy.

• Power: no charging inside the cave. Charge everything before leaving town.

• Signal: no phone signal. No wifi. Tell family before the trip starts.

• Water: river level changes. Guides decide when to cross and when to wait.

• Mud: some sections are slippery. Walk slowly and keep distance from the person in front.

• Camp: porters set up tents before the group arrives.

• Food: meals are cooked at camp. Snacks still useful for long walking days.

• Toilets: composting toilet system. All waste is carried out.

• Conservation: do not touch cave pearls, fossils, stalagmites or flowstone.

• Fitness: train with stairs, hills and a backpack. Flat-road walking is not enough.

• Timing: arrive in Phong Nha one day before briefing.

• Weather: January to August is the normal operating season. September to December is closed.

• Transport: Dong Hoi is the closest airport and train station, about 45 minutes by road.

• Backup trip: if Son Doong is full, check Hang En, Tiger Cave, Hung Thoong or Tu Lan.

On the route, the first day is not only about distance. The heat outside the cave can be tiring, then the river crossings cool the body quickly. Inside the cave, the air feels different again. Most guests remember the change from jungle to dark cave more than the number of kilometres.

At camp, keep personal items together. Sand, mud and wet clothes make it easy to lose small things. Headlamp should be easy to reach at night. A spare battery is better than searching in the dark.

The Great Wall of Vietnam is the final big obstacle. It is climbed with safety equipment, but guests still need to be calm with height and follow instructions. This is not a place to rush.

Son Doong is expensive and difficult to book, but the strict limit is part of the protection. Fewer visitors means less damage inside the cave and more work for the local support team.

Route rhythm:

• Briefing day: check gear, confirm health information, ask about shoes and waterproof packing.

• Morning start: breakfast early, then transfer from Phong Nha with the guide team.

• Jungle walking: expect heat, roots, narrow trail and some steep ground.

• River crossings: step slowly. Use poles or guide support when needed.

• Lunch stops: simple food, short rest, then continue before the body cools down too much.

• Cave entrance: helmets and headlamps become important from this point.

• Dark passage: walk in a line. Do not point headlamps into another guest's face.

• Photography: difficult in the big chambers. Small people in the frame help show scale.

• Campsite: keep wet clothes away from dry sleeping clothes.

• Night inside cave: darker than normal camping. Headlamp nearby before sleeping.

• Morning inside cave: pack early. Porters need time to clear camp.

• Doline sections: sunlight can be strong when the weather is clear.

• Forest inside cave: path may be slippery after rain.

• Fossil area: look, but do not touch the wall.

• Cave pearls: stay on the path. They are fragile and protected.

• Great Wall climb: listen to the safety briefing before starting.

• Exit day: legs may feel tired on the last jungle section.

• Return to town: keep one quiet evening in Phong Nha if possible.

Small items often forgotten:

• Lip balm.

• Plaster for hot spots on feet.

• Personal medicine.

• Insect repellent for jungle sections.

• Small towel.

• Spare socks.

• Waterproof phone pouch.

• Camera cloth for mist and condensation.

• Lightweight sleep clothes.

• A little cash left in Phong Nha for after the trip.

Good expectations make the trip easier. Son Doong is not clean all the time, not dry all the time, and not comfortable in the way a hotel tour is comfortable. The reward is the size of the cave, the silence in the large passages, the camps under the limestone roof and the feeling of walking through a place that only a small number of people can visit each year.

Leave in Phong Nha:

• Heavy laptop.

• Extra shoes not needed on the route.

• Jewellery.

• Large wallet.

• Hotel keys if the hotel can keep them.

• Big power bank, unless the operator allows it.

• Clothes for after the trip.

• Passport original, if a copy is enough for the expedition paperwork.

After the expedition, most visitors want a shower, laundry and a quiet meal. Do not plan a tight bus or flight connection straight after returning from the cave. The group may come back tired, muddy and later than expected if the trail or river takes more time.

Son Doong Cave in media and world records

After the 2009 survey, Son Doong became internationally known. National Geographic covered the cave and helped introduce it to a wider audience. In 2013, Guinness World Records recorded it as the largest natural cave.

On April 14, 2022, Google displayed a Doodle about Son Doong, showing the famous sunbeam in Doline 1. In March 2026, CBS aired a 60 Minutes segment about Son Doong Cave, including its discovery, ecosystem and the difficulty of filming inside such a huge underground place.

Son Doong also changed tourism in Phong Nha. Before adventure cave tourism developed, many local people had fewer tourism jobs and some still depended on forest work. After Son Doong became known, more homestays, transport services, restaurants and cave tours opened. The documentary "Son Doong: The Cave That Built a Village" tells how the cave helped change the local economy.

Other caves near Son Doong

Son Doong is the biggest cave in Phong Nha, but it is not the only cave expedition in the national park. More than 400 caves have been surveyed in the region, and experts say only part of the limestone massif has been explored.

If Son Doong is fully booked, above budget, or too physically demanding, there are other cave tours in Phong Nha with jungle trekking, camping, river crossings and large cave passages.

Hang Pygmy Cave is the fourth-largest cave in the world. The Hang Pygmy tour is shorter and includes cave camping inside the chamber.

The Tiger Cave system includes Hang Pygmy, one of the largest caves in the world, and the Kong Collapse area. This route suits visitors looking for a remote and physical jungle expedition.

The Hung Thoong expedition covers a wild cave system with river swimming, jungle camping and several caves connected by forest trails. The Tu Lan cave system is another option for underground rivers, swimming and camping near clear jungle lakes.

For more choices, visitors can read this guide to the top caves in Phong Nha.

Phong Nha - Ke Bang National Park

Son Doong Cave is inside Phong Nha - Ke Bang National Park, near the Vietnam - Laos border. UNESCO recognized the park as a World Natural Heritage Site in 2003 for geology and geomorphology, and again in 2015 for biodiversity.

Phong Nha - Ke Bang covers 123,326 hectares on the Vietnam side and contains the largest limestone massif in Southeast Asia. More than 400 caves have been found and surveyed, with more than 220km of measured cave passages. Cave experts continue exploration, and new caves are still found from time to time.

During the Vietnam War, many caves in Phong Nha were used by Vietnamese soldiers to store weapons, food and equipment, and to shelter from bombing. Because of this, some caves in the park have both natural value and war history.

In 2025, UNESCO approved the expansion of the World Heritage Site to include Hin Nam No National Park in Laos. This created the transboundary World Heritage property named Phong Nha - Ke Bang National Park and Hin Nam No National Park.

Getting to Phong Nha is straightforward. Dong Hoi has domestic flights and train connections. From Dong Hoi, Phong Nha town is about 45 minutes by road.