Sinkholes or giant holes that appear naturally, exist in many places. But this one is special because it's so big. It is located in Chongqing, China, and is named Xiaoxhai Tiankeng.
Some experts have wondered if this mysterious sinkhole formation was the result of a meteorite crashing into Earth. Others believe it gradually formed over about 128,000 years, as water seeping into an underground river slowly 'carved' into the surrounding limestone.
As quoted by us from the BBC, one thing is certain, with an estimated depth of 660 meters and a volume of 130 million cubic meters, Xiaoxhai Tiankeng is the deepest and largest sinkhole in the world.
Tiankeng means Heavenly Hole. This sinkhole is home to an ecosystem of around 1,285 species of plants and animals. In the rainy season, waterfalls cascade from the mouth of the hole, into an underground river and a network of caves at the bottom.
Locals have known about the sinkhole for centuries and were discovered by the outside world in 1994, when British explorers attempted to survey the area's maze-like underground cave system.
Although experts have tried to map the underground river five times over a 10-year period, the torrent was too difficult to navigate and failed.
So as a result, this dark and deep underground world remains one of China's great geological mysteries. There is still much that is not known about the sinkhole until now.