Introduction to the tiankeng: The Dragon Tank is an oval tiankeng with a long axis of 350 meters, a short axis of 170 meters and a depth of 550 meters. This depth ranks third in China and fifth in the world. The inner wall of the tank is like a chip, with pines and cypresses lying across the cracks in the wall, and ancient vines hanging upside down. The bottom of the tank is green all year round, and hundreds of birds are singing. Because it is shaped like a natural large stone tank, there is also a wonderful legend about the love between the woodcutter and the dragon girl, so it is named the dragon tank. It is also known as "the best tank in the world".