Introduction to the primeval forest at the bottom of the pit: The primeval forest at the bottom of the Dashiwei pit covers an area of about 96,000 square meters. It is the largest underground primeval forest in the world. The trees in the forest are thick and towering, and shrubs are growing there. Some of them are as old as the dinosaurs. There are short-gut ferns, rare green orchids, and the thorny square bamboo with an area of more than 500 square meters discovered for the first time in my country. There is an underground river in the forest. The fish and shrimp in the river have evolved uniquely because they have not seen the light of day for many years. There are many rare animals such as blind fish, white eagle, transparent shrimp, Chinese creek crab, ghost spider and so on. In order to protect the natural ecological environment of the tiankeng, tourists are prohibited from going down to the bottom of the pit.