This underground cave system is so large, it has own weather system

Stretching 42 kilometres under Southwest China, the Er Wang Dong cave system contains its own forests, rapids, and yes, clouds.

Explored in its entirety just last year, Er Wang Dong (meaning “Second Royal Cave”) is an enormous cave system in the Chongquing province of Southwest China. With passages stretching 42,139 metres (138,251 feet) and a maximum depth of 441 metres (1,447 feet), the cave is so large, it has its own lush green forest, crystal clear pools and white water rapids, enormous stalagmites, and oddly enough, clouds. 

While local nitrate miners knew there was something big lurking beneath China's 195-metre-deepNiubizi tiankeng sinkhole, it was only when a team of 15 explorers and photographers from the Hong Meigui Cave Exploration Society plumbed the depths of the sinkhole to access and explore the Er Wang Dong cave system that its sheer size was realised. Until the explorers got there, none of the system’s major underground passages had ever been touched by light.

Formed by limestone dated to the the Ordovician Period, which lasted almost 45 million years, from 488.3 million to 443.7 million years ago, Er Wang Dong is situated near another large cave system called San Wang Dong, with a length of around 67,825 metres.

One of Er Wang Dong’s strangest features is an area called the Cloud Ladder Hall, which takes up about 12.5 acres of space, capped by a thick layer of cloud and fog. 

"I had never seen anything quite like the inside cloud ladder before," said one of the team, UK-based photographer and caver Robbie Shone, according to Wunderground. "Thick cloud and fog hangs in the upper half of the cave, where it gets trapped and unable to escape through the small passage in the roof."

The clouds form within the caves when the humidity from the ground rises up into the cavern’s cooler air above. 

"It is always very special, knowing that you are the first to step foot into a cave or somewhere where nobody had previously seen, not knowing what you might find and discover," said Shone. "Where else on Earth can still hold secrets and mysteries of discovery? That's what I love so much about exploring."