Plants are seen inside a sinkhole in the mountainous Xuanen County in central China's Hubei Province, May 19, 2015. Due to the local Karst landscape and humid climate, a sinkhole more than 290 meters deep in Xuanen has become home for various plants and animals. A full and original eco-system is kept in the hole as it is hard for human to get in. (Photo: Xinhua/Yang Shunpi)