China’s “heavenly pits”, a dive into the unknown

In 2016, in Baise Leye County of Guangxi Zhuang Autonomous Region of China, my team and I rappelled down with a rope to the bottom of the Dashiwei Tiankeng, 600 metres under the ground. The term tiankeng, “heavenly pit”, refers to large sink-like negative terrains with steep walls, formed over millions of years and developed in carbonate rock strata.