Hang Son Doong (Mountian River Cave), the largest natural cave in the world, is located right in the heart of Phong Nha-Ke Bang National Park in the Quang Binh province of Vietnam. It was formed during the Cambrian-Permian geological eras, putting it at a date between 400–450 million years old.
It stretches for over three miles (five kilometers), and it reaches heights of 650 feet (200 meters). The main cavern is large enough to house an entire New York City block.
What’s even more amazing is that the ecosystem created within the cave has its own weather system and creates its own clouds. Inside, you will find the largest stalagmite known to man, hanging at 262 feet tall (80 meters), and fossils dating back millions of years.
Collapsed ceilings have created openings known as dolines, and this has allowed foliage to grow inside the cave. You will come across jungles and rivers enveloped by misty clouds, and microorganisms thriving in the darkness. It is a whole other world, devoid of much human interaction. You will be walking into an image of Earth as it was hundreds of million of years ago.
According to theculturetrip