Er Wang Dong

Er Wang Dong (Chinese: 二王洞; literally: "Second Royal Cave") is a large cave in the Wulong Karst region, in Wulong County of Chongqing Municipality of China.

Current known length of its passages is 42,139 metres (138,251 ft) with a maximum depth of 441 m (1,447 ft). It is large enough to contain its own weather system. The cave starts in the 195 m (640 ft) deep Niubizi tiankeng (牛鼻子天坑; "ox nose sinkhole") and also contains the 295 m (968 ft) deep Qingkou tiankeng.

Er Wang Dong cave has formed in Lower Ordovician limestone and is located close to another very large cave system - San Wang Dong.

Both caves were explored by Hong Meigui Cave Exploration Society. Local people make weather forecasts based on the observations in Niubizi tiankeng - if there is a fog coming from the cave, rain is expected.