Global Traveler

Step inside one of the largest — and most beautiful — caves in the world

Son Doong Cave V2

Discover:
Vietnam's colossal
Son Doong Cave

First explored in 2009, Hang Son Doong is one of the largest caves in the world.

Only 1,000 travelers are allowed to explore it every year.

Here's what they see.
The story of Son Doong
I

n 1990, a local man named Ho Khanh stumbled upon a cave deep in the jungles of central Vietnam. Wind and vapor-like clouds emerged from the entrance, and the sound of a river could be heard in the distance.

He did not go in.

Five years later, he sat one evening with Howard Limbert, a traveler who had hired him as a guide and porter. Speaking little English, Ho Khanh drew pictures in the sand of the cave entrance he had seen.

He drew the wind, the clouds and the water — all signs Howard knew indicated a massive cave in their midst.

That was the start of a 14-year endeavor by the duo to re-locate what is now known as the Son Doong cave.

The search for the elusive cave
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oward and his British caving team knew that a sizable cave likely existed within central Vietnam’s Phong Nha-Ke Bang National Park. A local river disappeared into the ground and reemerged six miles away. The water had to flow somewhere.

But where?

The easiest way to find a cave is to follow a river straight into it. But long ago huge boulders had collapsed where the river disappeared into the earth. The U.K. team led three expeditions to find the cave — and failed each time.

Alone, Ho Khahn set out to find the elusive cave entrance once again. Notching trees to mark his way, he wandered in the jungle for a week.

When Howard returned to Vietnam in 2009, Ho Khahn — speaking through a translator — told him the good news.

Meet Howard and Ho Khahn

Howard Limbert is a British cave expert who has explored thousands of caves around the world — nearly 600 in Vietnam alone. In the 1990s, he began making annual caving trips to Vietnam with fellow members of the British Cave Research Association.

Ho Khanh is a Vietnamese logger born in the rural hills of Phong Nha, an area then ravaged by starvation and malaria. After losing his father in the Vietnam War (or the “American War” as it is known in Vietnam), Ho Khanh began foraging for precious wood to earn money for his family. In turn, he became a master of the jungle.

In 1995, Howard hired Ho Khanh as a guide and porter for his team’s annual caving expedition to Vietnam. The British team hired many local people, but Ho Khahn stood out.

“We realized he was brilliant in the jungle.”

- Howard Limbert

A jungle secret rediscovered
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o Khahn had found the entrance by scrambling 300 feet up the side of a mountain. Howard, his wife Deb (a fellow caver) and the rest of the British team were ecstatic. They immediately set out for the entrance, with Ho Khahn at the helm.

“As we got near, we could see clouds and wind pouring out of the cave. The trees were all bent at 45 degrees,” said Howard.

They didn’t know it then, but the entrance ahead of them would reveal one of the largest caves in the entire world.

Stepping into Son Doong
H

ang Son Doong, which translates to “mountain river cave,” is in central Vietnam in an area that was once part of the Ho Chi Minh Trail.

Its main tunnel passage is over three miles long, and its largest sections are 650 feet high and 500 feet wide. An entire New York city block can fit inside.

Only 1,000 tourists are allowed to visit each year, and Oxalis Adventure is the only company with permission to take travelers inside.

From January to August, small groups (up to 10 people) embark on four-day treks through the cave. The trek is classified as moderate to difficult and covers 18 miles of rocky, and sometimes wet, terrain.

Day 1
T

he expedition begins with a five-hour hike, with a stop in the isolated village of Ban Doong — population 40 — and numerous river crossings along the way.

The Vietnamese porters each carry around 70 pounds of equipment; customers carry their water bottles and cameras. For those formerly working in the logging industry, this amount of weight is “easy” for them, says Howard, as they are accustomed to carrying twice that amount through the jungle.

“The Vietnamese are outrageous when it comes to strength and balance. They are trustworthy and loyal people — they are the best,” said Howard.

Day 1

Finally, a cave appears. Only it’s not Hang Son Doong — it’s Hang En (“hang” means cave in English). Hang En is a beautiful cave with a glittering lake in an enclosed valley; trekkers must go through it to reach Hang Son Doong.

It’s a gorgeous place to swim.”
- Howard
Day 1

The camp breaks here for the night. While porters set up mats and sleeping bags in individual tents, trekkers can bathe — in bathing suits — in the lake.

Day 1
T

he expedition begins with a five-hour hike, with a stop in the isolated village of Ban Doong — population 40 — and numerous river crossings along the way.

The Vietnamese porters each carry around 70 pounds of equipment; customers carry their water bottles and cameras. For those formerly working in the logging industry, this amount of weight is “easy” for them, says Howard, as they are accustomed to carrying twice that amount through the jungle.

“The Vietnamese are outrageous when it comes to strength and balance. They are trustworthy and loyal people — they are the best,” said Howard.

Finally, a cave appears. Only it’s not Hang Son Doong — it’s Hang En (“hang” means cave in English). Hang En is a beautiful cave with a glittering lake in an enclosed valley; trekkers must go through it to reach Hang Son Doong.

“It’s a gorgeous place to swim,” said Howard.

The camp breaks here for the night. While porters set up mats and sleeping bags in individual tents, trekkers can bathe — in bathing suits — in the lake.

Day 2

Greeted by a 200-foot drop, trekkers descend into Son Doong using ropes and harnesses. Technical rappelling experience isn’t required.

“It’s not just the size that makes Son Doong remarkable, it’s the beauty.”
- Howard
Day 2

Temperatures are cooler at the bottom of the cave, which typically holds steady at 73 degrees F, give or take a degree or two.

Day 2

Son Doong’s size is owing to two main factors: the river that runs through it, shown above, and the fault line upon which it sits, shown below.

Day 2

Staying dry is not an option on this trek; trekkers cross the river two times while in Son Doong.

Spelunking is an American term. The rest of the world calls it caving.”
- Howard
Day 2

The size and features of Son Doong make it popular with travelers, filmmakers (notably, as the home of King Kong in 2017’s “Kong: Skull Island”) and world-class spelunkers.

Day 2

The cave is estimated to be 2.3 million years old — relatively young considering the surrounding limestone is 400 million years old.

Day 2

This giant stalagmite is called the Hand of Dog.

A woman on our original expedition asked if she could name it. She shouted ‘The Hand of God,’ and the lad who wrote it down wrote ‘Hand of Dog’ instead. We didn’t know it was going to be famous, so some names are a bit weird.”
- Howard
Day 2

No part of the cave is flat but for the campsites, as evidenced here through “Fossil Passage” where 350 million-year old white fossils stand out against the dark limestone.

Day 2

Ahead is one of Son Doong’s greatest assets – the first of two dolines, or sinkholes …

Day 2

… which let mesmerizing beams of light penetrate the cave.

Day 2

Son Doong is so big, it has its own weather system. Sun from the doline heats the river water, which forms clouds within the cave.

Day 2
S

unlight always pours into Hang En, but beams like this only exist from December to March. American Ryan Deboodt, who has photographed Son Doong 10 times, explained how he shot this image.

“On this morning, my friend Thanh and I woke up to a cloudy sky. We decided to stay behind, hoping that the sun would break through. We waited and waited. Eventually the clouds broke, and the glorious sunbeam poured through the entrance. I ran around like a maniac for the next 15 minutes capturing as many photos as I could.”

The journey continues through Hang En, back into the jungle…

… towards the relatively small entrance to Son Doong cave, an attribute which helped keep it hidden for so long.

Greeted by a 200-foot drop, trekkers descend into Son Doong using ropes and harnesses. Technical rappelling experience isn’t required.

“It’s not just the size that makes Son Doong remarkable, it’s the beauty,” said Howard.

Temperatures are cooler at the bottom of the cave, which typically holds steady at 73 degrees F, give or take a degree or two.

Son Doong’s size is owing to two main factors: the river that runs through it, shown above, and the fault line upon which it sits, shown below.

Staying dry is not an option on this trek; trekkers cross the river two times while in Son Doong.

The size and features of Son Doong make it popular with travelers, filmmakers (notably, as the home of King Kong in 2017’s “Kong: Skull Island”) and world-class spelunkers.

“Spelunking is an American term. The rest of the world calls it caving,” said Howard.

The cave is estimated to be 2.3 million years old — relatively young considering the surrounding limestone is 400 million years old.

This giant stalagmite is called the Hand of Dog.

“A woman on our original expedition asked if she could name it. She shouted ‘The Hand of God,’ and the lad who wrote it down wrote ‘Hand of Dog’ instead. We didn’t know it was going to be famous, so some names are a bit weird,” said Howard.

No part of the cave is flat but for the campsites, as evidenced here through “Fossil Passage” where 350 million-year old white fossils stand out against the dark limestone.

Ahead is one of Son Doong’s greatest assets – the first of two dolines, or sinkholes …

… which let mesmerizing beams of light penetrate the cave.

Son Doong is so big, it has its own weather system. Sun from the doline heats the river water, which forms clouds within the cave.

The second day of the trek ends at the bottom of the doline, where travelers can bathe in a lake a short walk from the campsite.

Day 3
T

he third day begins with brilliant beams of morning light piercing through the doline. The trek continues across the first doline, with the previous night’s campsite visible in the background. Along the way, trekkers pass a huge bomb casing (“probably 3,000 kilos”) dropped during the Vietnam War.

Day 3

Nobody has seen the top of Son Doong’s dolines in person; the jungle is dense, and the limestone is sharp. A drone captured this image of the doline from above.

Day 3

Natural holes develop in the walls that are large enough to walk through.

Day 3

An hour later, the second doline appears. One of the most spectacular sights in Son Doong, this doline is huge — nearly as wide as the Mercedes-Benz Super Dome in New Orleans — and allows enough sunlight into the cave for a jungle to grow 820 feet below the ground.

Day 3

Plants and animals flourish here in the jungle known as “The Garden of Edam.” Trees can grow over 150 feet tall, and monkeys, snakes and at least one eagle owl (over three feet tall) call it home. Two types of flightless birds scamper around. “We don’t have a clue how they got in there,” said Howard.

Caves are really stable; they are not like mines. Son Doong may collapse but not in our lifetimes — maybe in one million years or so.”
- Howard
Day 3

Camp is set up here for the night, where moonlight pours into the cave through the doline, which likely fell some 500,000 years ago.

Day 3
T

he third day begins with brilliant beams of morning light piercing through the doline. The trek continues across the first doline, with the previous night’s campsite visible in the background. Along the way, trekkers pass a huge bomb casing (“probably 3,000 kilos”) dropped during the Vietnam War.

Nobody has seen the top of Son Doong’s dolines in person; the jungle is dense, and the limestone is sharp. A drone captured this image of the doline from above.

Natural holes develop in the walls that are large enough to walk through.

An hour later, the second doline appears. One of the most spectacular sights in Son Doong, this doline is huge — nearly as wide as the Mercedes-Benz Super Dome in New Orleans — and allows enough sunlight into the cave for a jungle to grow 820 feet below the ground.

Plants and animals flourish here in the jungle known as “The Garden of Edam.” Trees can grow over 150 feet tall, and monkeys, snakes and at least one eagle owl (over three feet tall) call it home. Two types of flightless birds scamper around. “We don’t have a clue how they got in there,” said Howard.

Camp is set up here for the night, where moonlight pours into the cave through the doline, which likely fell some 500,000 years ago.

“Caves are really stable; they are not like mines. Son Doong may collapse but not in our lifetimes — maybe in one million years or so,” said Howard.

Day 4
T

he final day gives the best view of Son Doong’s unusually large cave pearls, some of which are as big as baseballs. They are formed when water droplets rotate grains of sand, turning them over and over causing concentric layers of calcite to develop.

The darkness of Son Doong is both challenging and fascinating. Photography is difficult as lighting must be brought into the cave; one photo can take hours and up to 10 people to create.

Conversely, the lack of light has allowed new life to develop. Seven new species — all of which are completely white — have been found in the cave: fish, spiders, centipedes, woodlice and more. As they live in total darkness, they do not need color to blend into their surroundings. The fish have translucent skin, and some of the insects no longer have eyes.

Day 4

In the rainy season, a lake nearly 2,000 feet wide forms in the cave. By June, it disappears.

Day 4

The lake sits near the final push to exit Son Doong, a 300-foot vertical cliff nicknamed “The Great Wall of Vietnam.”

Day 4

The wall is climbed using ropes and a 65-foot ladder. Before the ladder was installed, trekkers had to turn back and exit through Hang En. The introduction of the one-ton ladder decreased the physical impact on the cave and shortened the trek by two days.

Day 4

At the top of the wall, trekkers eat lunch before crossing an area of calcified bones left by animals that wandered into the cave but never left. Trekkers do leave Son Doong, exiting the cave about 20 minutes after this point.

Day 4
T

he final day gives the best view of Son Doong’s unusually large cave pearls, some of which are as big as baseballs. They are formed when water droplets rotate grains of sand, turning them over and over causing concentric layers of calcite to develop.

The darkness of Son Doong is both challenging and fascinating. Photography is difficult as lighting must be brought into the cave; one photo can take hours and up to 10 people to create.

Conversely, the lack of light has allowed new life to develop. Seven new species — all of which are completely white — have been found in the cave: fish, spiders, centipedes, woodlice and more. As they live in total darkness, they do not need color to blend into their surroundings. The fish have translucent skin, and some of the insects no longer have eyes.

In the rainy season, a lake nearly 2,000 feet wide forms in the cave. By June, it disappears.

The lake sits near the final push to exit Son Doong, a 300-foot vertical cliff nicknamed “The Great Wall of Vietnam.”

The wall is climbed using ropes and a 65-foot ladder. Before the ladder was installed, trekkers had to turn back and exit through Hang En. The introduction of the one-ton ladder decreased the physical impact on the cave and shortened the trek by two days.

At the top of the wall, trekkers eat lunch before crossing an area of calcified bones left by animals that wandered into the cave but never left. Trekkers do leave Son Doong, exiting the cave about 20 minutes after this point.

So, is Son Doong the largest cave in the world?

Might a cave bigger than Son Doong exist?

“I’d like to think so, but it’s unlikely. Anything bigger would probably collapse. Vietnam has the best chance. We’ve only explored about 30% of the country, so you never know,” said Howard.

Where are Howard and Ho Khahn today?

Howard is the Technical and Safety Director at Oxalis Adventure. He now lives in Vietnam fulltime and continues to explore new caves in the country.

Ho Khahn leads the porter teams for Oxalis Adventure. He is highly respected in his village and has used his work at Hang Son Doong to build a beautiful home by the river, a portion of which he operates as a homestay for caving travelers.

As for the area around Phong Nha, what was once one of the poorest parts of Vietnam is now thriving. An estimated 5,000 local Vietnamese are currently employed by the tourism industry, which is anchored by the area’s magnificent cave systems.

T

he answer isn’t exactly clear. Some caves have passages that are narrow but long (Kentucky’s Mammoth Cave) while others have enormous chambers (China’s Miao Room and Borneo’s Sarawak Chamber).

However…

A narrow underwater passage near the first doline is believed to connect to a nearby cave, Hang Thung, a fact which Howard said that, if true, would establish Son Doong as the largest cave in the world. To determine if the caves connect, a dive is planned for March of 2020 and will include British diver John Volanthen, one of the first divers to reach the Thai soccer team trapped in the Tham Luang cave complex in 2018.

“We know it joins; we’ve tested the waters. But we won’t count it until we physically dive it ourselves,” said Howard.

Credits

Writer: Monica Buchanan Pitrelli
Design and code: Bryn Bache
Editor: Ted Kemp
Images and videos: Oxalis Adventure and Ryan Deboodt Photography