Introduction to tiankeng and floor drains: is located in an area of more than 300 square kilometers in the Yanbian rock mouth and depression area. There are more than 1,000 funnel groups of different diameters and depths. The larger funnel group is about The area is more than 5,000 square meters and the depth is about 30 meters. The smaller area is about more than 400 square meters and the depth is different.