Cave expedition members rest at the bottom of a Tiankeng (an area of naturally formed pits) in Napo County, south China's Guangxi Zhuang Autonomous Region on Nov 2, 2019. [Photo/Xinhua]

The photo shows the scene at the bottom of Nongyang Tiankeng (an area of naturally formed pits) in Napo County, south China's Guangxi Zhuang Autonomous Region on Nov 2, 2019. [Photo/Xinhua]

A cave expedition member works in a cave in Napo County, south China's Guangxi Zhuang Autonomous Region on Nov 5, 2019. [Photo/Xinhua]