Son Doong: The Largest Cave in the World (Contains a Rainforest!)

Son Doong Cave Entrance
© Vietnam Stock Images/

Written by Jude Speegle

Published: April 29, 2022

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Walking along the terrain of the Phong Nha-Ke Bang National Park in Vietnam, you encounter a cave entrance. Stalagmites and stalactites pepper the mouth like awkward teeth, and clouds of steam emerge in plumes of hot breath.

The darkness is absolute once you enter. There is a steep decline to follow at first until it leads you further into the cave. Son Doong, the world’s largest cave, is known for having fantastic structures and unique sights, though you can’t see it without your own light. No sunlight reaches this cave’s innards.

Son Doong has been unrevealed for thousands of years, millennia even. Never did a foot touch the workings of this cave until 2009, when a team of British explorers made landfall, so to speak.

Discovering the Largest Cave in the World

Largest Cave in the World - Son Doong

Son Doong in Vietnam is the largest cave in the world.

©David A Knight/

This cavern has existed for more than 3 million years, expanding and playing host to its secret society of life. It was initially discovered by a local man in Vietnam, Ho Khanh. 

In the early 1990s, Ho Khanh sought to gather wood or food deep in the Phong Nha-Ke Bang National Park. He found a cliff made of limestone and followed it to discover the opening to a never before seen cave. He saw clouds emerging from the cave entrance and a river’s sounds within. 

Focused on his need to make a living, he left the cave and promptly forgot about it for nearly twenty years. The British Cave Research Association searched the area for caves in the early aughts, and Ho Khanh mentioned the one he had come across.

Eager for new discoveries, the British cavers encouraged him to try and find it again, which he eventually did. Once he had again located the entrance to the cavern, he revealed that information to the cavers.

Exploring Son Doong

Son Doong Cave, Vietnam

The first person to enter Son Doong was British explorer Peter MacNab


It was the morning of April 7, 2009, when Peter MacNab was the first person ever officially to enter the mouth of Son Doong cave. To follow were other intrepid explorers, eager to now map out something entirely new.

Caverns are measured in many different ways; by depth, length, width, and volume. Son Doong is measured as the largest cave in the world by volume, measured by all the empty space and the entire shape. So the area within the cavern and growths is calculated in cubic meters.

In 2009, after the initial exploration, San Doong was estimated to be 38.5 million cubic meters, making it the largest cave in the world. It had taken only a week to come to this conclusion.

They measured this cave by cross-section, meaning straight cuts are made through the cave, usually at right angles. When measured by cross-section and calculated at volume, Son Doong truly is the most extensive cave on the planet.

Some passages within Song Doong go through periods where they are flooded, forming underground lakes or muddy areas.

Formed By An Underground River

Son Doong River

Son Doong cavern was formed by its underground river over millions of years, which runs through its length.

©Hoang Trung/

Once you’ve dropped in over the initial hurdles, you see the beginnings of the river deep within Son Doong. This river is the very same one that has traversed beneath the ground for thousands of years, forming the cavern. Son Doong exists because this river has surged through it and assembled it.

Son Doong is more than just exciting because of its immense size; it is also home to a few fascinating structures called dolines. A doline is a sinkhole. It is a depression in the earth that is closed when all the rock that fell forms a base. It otherwise would sink deep within the earth.

A doline is formed when the roof of a cave collapses, and Son Doong has two massive dolines that let sunlight leak into the cave’s depths. This allows plant growth and vegetation, leading to one of the world’s only underground rainforests that we have discovered.

Known as the “Garden of Edam,” this rainforest is more than 200 meters, or 656 feet, beneath the earth’s surface, and it is thriving. Due to the unique circumstances of its existence, this rainforest has its own ecosystem and weather system. 

There are many unique animals that make their homes within this jungle, and trees extend hundreds of feet upwards. Due to only having been explored in recent years, not much is known about the animals within the cave.

Son Doong is also known for the “Great Wall of Vietnam,” a 90-meter-high calcite barrier at one edge of the cave. This translates to 295 feet of rock to traverse in a slick and darkened environment with specialized equipment.

Larger Than Originally Believed

Son Doong Cave Entrance

Son Doong is a whopping 1.35 billion cubic feet.

©Vietnam Stock Images/

In April of 2019 a British team of explorers went diving in Son Doong and discovered that the world’s largest cave extended even further than previously thought. There is actually a connecting pathway from Son Doong to another cavern known as Hang Thung.

Thus, Son Doong cave extends to 1.35 billion cubic feet, once again making it the largest cave in the world. 

The river’s origins that created this brilliant piece of nature are still unknown. There may be another larger cave connected that hasn’t been discovered yet or a body of water that hasn’t been figured out.

Regardless of how this massive cavern came to be, it is still a startling example of the mysteries of nature. There is so much still unknown to us, and we can explore and discover for another thousand years and never know fully what the earth has to give us.

Son Doong is a testament to the solidity and perseverance of nature. Even when we aren’t watching, it exists, it expands, it creates.

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About the Author

Jude is a writer both by trade and by heart. They have been writing since a very young age and have eight years of professional writing experience. Passionate about animals, Jude has three birds and three cats.

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