Shuanghedong, is the longest cave in China, in Asia, and the 6th longest in the world in 2018. 

It is located near the town of Wenquan in Suiyang County, Guizhou Province. 

This gypsum and dolomite cave has carbon dioxide levels of approximately 400ppm, with a constant temperature of about 13 degrees Celsius year round.

The cave contains numerous waterfalls, and at least three underground rivers, some of which contain cave shrimp, and fish weighing several pounds. Also found, have been tadpoles, frogs, salamanders, insects, spiders, bats, leeches, blind fish, and mushrooms.

According to en.wikipedia