The Son Doong Cave in Vietnam is the world's largest cave passage created by water percolating down from a rainforest above. About 200 meters below ground level is a flourishing jungle inside, which is home to an impressive ecosystem. However, the rainforest is dangerous and accessible to only a few explorers and tourists.

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(Photo: NHAC NGUYEN/AFP via Getty Images)
A visitor takes part in a tour of Son Doong cave, one of the world's largest natural caves, in central Vietnam's Quang Binh province on January 19, 2021.

A Serendipitous Find

Ho Khanh, a farmer in central Vietnam, came across a small entrance to what was now known as the world's largest cave system when he sought shelter from a storm. He reported his discovery to the British Caving Research Association, but since he forgot his trail, it took almost two decades to explore.

According to Travel Awaits, Khanh discovered the cave in 1991, but it wasn't until 2009 that the cave was explored for the first time. After the first expedition, Son Doong Cave was crowned the largest in the world. Divers discovered in 2019 that Son Doong Cave is linked to another cave, Hang Thung, making the cave system much more complex.

Son Doong Cave is located in the Quang Binh province of Central Vietnam. Hang Son Doong, which means Mountain River Cave, is positioned about 30 miles northwest of Dong Hoi, a city on the coast of Vietnam.

Estimated to be 3 million years old, it has a total length of nearly 9 km long and 1.35 billion cubic feet large enough to fit 40 skyscrapers. A Boeing 747 can comfortably fly through its largest passageway. It is reportedly five times larger than the Deer Cave in Malaysia, which was the largest natural cave before the discovery of Son Doong Cave.

While no evidence exists that humans explored the cave before the 2000s, other forms of life made their way there. Snakes, flying foxes, monkeys, squirrels, birds, and rats have been found inside the cave, as well as seven new species of white, eyeless creatures, such as spiders, fish, scorpions, and shrimp. The cave also has a weather system, rainforest, and unique limestone cave pearls on display.

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Son Doong Cave's Own Weather System

Son Doong Cave is situated within Phong Nha-Ke Bang National Park, and thus its climate and weather are influenced by the prevailing conditions in the park, as per Oxalis Adventure Tours.

Despite this connection, Son Doong has its own separate climate and weather system, which is one of the reasons it is so renowned. Its climate can be observed and experienced by those who venture into the cave.

The cave's climate transforms with each season. For example, visitors to Son Doong can expect to see clear views between February and April, with the sunlight streaming through the collapse and creating stunning visual displays. Although the weather during this period can be a little chilly, the Sun elevates the overall experience.

During June through August, visitors may notice clouds forming within Son Doong Cave, particularly near the first campsites of Doline 1 and Doline 2. The warmth emanating from the doline, an open-air depression in the ground, combines with vapor from the underground river in the cave, producing a misty, dreamlike sight.

Rainfall can wash the weather clean, but gaps in the cave roof allow water to seep in and flow over the nearby dolines, creating splendid waterfalls. The weather can vary as visitors cross the dolines, but Son Doong remains notably cool even during summer.

Finally, visitors can expect cool winds blowing through the cave in winter. The unique weather and climate conditions within Son Doong Cave offer an experience of the changing seasons that is unlike any other.

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