Inside the Largest Cave in the World: Hang Son Doong

^{Disclosure: This post may contain affiliate links, meaning I get a commission if you decide to make a purchase through my links, at no cost to you.}

Did you know that the largest cave in the world is so huge it could fit an entire New York City block inside? Welcome to Hang Son Doong, a jaw-dropping wonder hidden in the depths of Vietnam. This underground offers a glimpse into a world that seems almost alien in its beauty and scale.

The Discovery of Hang Son Doong

The story of Son Doong Cave starts in 1990. A local man named Ho Khanh stumbled upon its entrance while searching for valuable agarwood in the dense forests of Phong Nha-Ke Bang National Park. Ho Khanh got caught in a thunderstorm and sought shelter. He found himself at the base of a cliff, where he noticed something unusual. A strong wind was blowing out of an opening, and he could hear the sound of rushing water deep below. This chance encounter marked the first sighting of what would later be known as the largest cave in the world.

Despite his remarkable find, Ho Khanh didn’t think much of it at the time. It wasn’t until 17 years later, when he mentioned his discovery to members of the British Cave Research Association (BCRA), that the true significance of the cave began to emerge. The BCRA had been exploring caves in Vietnam since 1990 and were eager to investigate this new lead.

In 2009, Ho Khanh led an expedition from the BCRA to the cave entrance. On April 7th of that year, Peter MacNab became the first person to enter Son Doong Cave. The team was amazed by what they found. The cave’s enormous size and unique features, including its own ecosystem, quickly became apparent.

The name San Doong was chosen by Mr. Khanh and the BCRA team. Son translates to mountain and Doong is the name of the valley where Rao Thuong stream flows through. Hang is the Vietnamese word for cave. This translates to the ‘Mountain River Cave’.

Exporing Hang Son Doong

The BCRA team faced numerous challenges when exploring Son Doong. The cave’s vast size and complex structure made mapping a daunting task. Using laser instruments, they carefully measured and surveyed the cave’s passages. Their progress was stopped by a massive 60-meter high flowstone-coated wall, which they named the “Great Wall of Vietnam.”

The team returned in March 2010 with specialized climbing equipment to get over the “Great Wall.”. During this visit, they successfully scaled the wall and discovered an additional quarter mile of enormous passage. This passage led to an exit in the jungle. This completed the first full exploration of Son Doong Cave.

The team’s measurements were astounding. Son Doong Cave stretched for over 5.6 miles in length, with a volume of 38.5 million cubic meters. These measurements confirmed it as the largest natural cave in the world, surpassing the previous record-holder, Deer Cave in Malaysia, by a significant margin.

Geological Wonders of Son Doong

Some sections of Son Doong cave are over 656 feet tall and, at their widest, are 525 feet. To put this into perspective, you could fit an entire New York City block inside, complete with skyscrapers! The cave is more than five times larger than its nearest competitor, Deer Cave, in Malaysia.

The sheer size of Son Doong has a significant impact on its environment. The cave has its own weather system, with temperatures ranging from 60-77 degrees Fahrenheit depending on the season. It is always cooler inside the cave than outside. Sometimes, the difference is by as much as 8 to 12 degrees in summer. This temperature difference, combined with the damp atmosphere and varying air pressure, causes unique airflows within the cave.

The cave is home to some of the tallest known stalagmites in the world, with some reaching heights of up to 262 feet! One awe-inspiring formation, nicknamed the “Hand of Dog,” stands nearly half a mile from the first sinkhole.

Son Doong has two massive skylights where the cave ceiling has collapsed. These openings allow sunlight to penetrate the cave, creating an environment where plants can thrive. The result is a lush, ancient forest known as the Garden of Edam, complete with trees reaching 100 feet tall.

The cave also boasts other unique formations. Cave pearls the size of baseballs have been discovered, an unusually large size for such formations. Another interesting feature is the presence of phytokarst, a type of limestone erosion caused by biological activity. This creates formations resembling pencil bundles, pointing towards the light source.

The Flora and Fauna of Hang Son Doong

The closed system inside Hang Son Doong, created by the cave’s distinctive climate, weather, sunlight, and humidity, supports a wide variety of life forms that have adapted to the challenging environment.

The cave’s flora is surprisingly rich, with over 200 plant species identified by biologists. These include herbal epiphytes, mosses, vines, shrubs, and even large trees reaching heights of up to 100 feet tall. The cave’s two dolines, or skylights, also play a crucial role in supporting plant life by allowing sunlight to penetrate the cave’s depths. This has led to the formation of primeval forests within the cave, such as the Garden of Edam in Doline 2.

The cave also houses diverse animal life, from tiny insects to larger mammals. Cave swiftlets dart through the vast chambers, navigating in complete darkness. White cave spiders, perfectly adapted to the low-light conditions, spin their webs in the shadows. Blind cavefish swim gracefully in the underground rivers, having evolved to live without eyesight.

Other notable inhabitants include cave crickets, beetles, and various bat species. These animals have developed unique adaptations to thrive in the cave’s environment, such as enhanced senses and, often, translucent bodies. Son Doong has been the discovery site for over seven new species, including fish, frogs, lizards, spiders, and scorpions.

The cave’s ecosystem also extends to larger animals. Flying squirrels, snakes, and monkeys have been observed in the forested areas near the dolines. There have even been sightings of a large bird, possibly an eagle or owl, flying around the sinkhole and inside the cave.

How Hang Son Doong Formed

The story of Son Doong begins over 400 million years ago when the limestone that would eventually house the cave was first created. This limestone, which forms part of the oldest and largest limestone massif in Southeast Asia, was formed from two sources: chemical precipitation of calcium carbonate from seawater and the accumulation of skeletal remains from marine organisms like shells, snails, and corals.

Over time, tectonic movements caused these limestone layers to rise, forming the mountains we see today. However, the creation of Son Doong Cave itself is a much more recent event, estimated to have begun between 2 and 5 million years ago.

The cave’s formation is primarily due to the erosive power of water. Rainwater, which becomes slightly acidic when it absorbs carbon dioxide from the air and soil, slowly dissolved the limestone along a fault line in the Truong Son mountain range. This process, known as karst formation, created a vast underground tunnel.

Two rivers, the Rao Thuong and Khe Ry, played a crucial role in shaping Son Doong. These underground waterways carved out the cave’s massive passages over millions of years. The Khe Ry is notable as the longest river cave in Asia.

As the cave grew larger, some areas of the ceiling became too thin to support their own weight. This led to collapses. Two massive dolines or skylights were created from these collapes and are some of the distinctive features of Son Doong. These openings allow sunlight to penetrate the cave, supporting the unique ecosystems found within.

Today, Son Doong Cave continues to evolve.

How To Visit Hang Son Doong

Visiting Hang Son Doong requires quite a bit of planning. Trekking is the only way to get there, and you must go with an approved travel company. This isn’t a place you can visit on a whim. The journey begins in Quang Binh, Vietnam, and the trek starts with a challenging 10.5-mile hike through rocky mountain trails and dense jungle. There are also river crossings, with some reaching waist-deep levels.

The trek is a two-day journey, and on the first night, hikers spend a night camping in the Hang En Cave. In this cave, you can swim in an underground lake!

Upon arrival at Son Doong’s entrance, visitors descend into the cave using harnesses. The journey involves about 5 miles of caving, including scrambling over rocks and navigating steep sections with the help of ropes and ladders. Highlights include the “Hand of Dog” stalagmite and the mesmerizing “Watch out for Dinosaurs” doline. The expedition culminates with conquering the “Great Wall of Vietnam,” a challenging 90-meter climb that rewards with breathtaking views.

Son Doong expeditions run from January to August with a limit of 1000 visitors per year. Securing a spot requires advance planning, often up to 18 months ahead.

Conservation and Sustainable Tourism

Strict measures have been put in place to limit visitor numbers. Currently, only 1000 people are allowed to explore the cave annually, making it an exclusive and highly sought-after experience. This approach has a significant impact on preserving the cave’s pristine state while still allowing for controlled tourism.

Oxalis Adventure, the sole company permitted to run tours of Son Doong, employs and trains local people, including Ho Khanh, the cave’s discoverer, who now leads the porter team. This not only benefits the local economy but also ensures that those most familiar with the area are involved in its protection.

The cave’s conservation efforts extend beyond visitor limitations. Strict guidelines are in place for those lucky enough to explore Son Doong. These include carrying out everything brought into the cave and following designated paths to minimize human impact. Such measures have successfully maintained the cave’s natural state, with its interior looking untouched despite hundreds of guided groups having passed through.

Once the tour group leaves, these are buried outside the cave, where they naturally decompose, leaving no trace of human presence.

There have been controversial plans for mass tourism development, including a proposed cable car system. However, many stakeholders advocate maintaining the current sustainable approach. This careful balance between conservation and tourism has protected Son Doong and contributed to preserving the surrounding Phong Nha-Ke Bang National Park. Sustainable tourism and heritage conservation can coexist for long-term development.