Giant karst sinkhole cluster found in Guangxi

"The exploration of the world-class sinkhole is full of thrills and challenges. However it is worthy as we have witnessed and learned extraordinary skills from French speleologists," Chen said.

With the help of the drone, French speleologist Bottazzi Jean found a sinkhole with a depth of over 270 meters and, once at the bottom, was puzzled by some unusual things: tomblike rock piles, some carved wood and unused firewood.