Introduction to the lower cave hall: is the "time and space tunnel". The cave hall is flat and oblique, about 120 meters long, 50 meters wide, 2 to 3 meters high, and covers an area of ​​about 6,000 square meters. The caves in the hall are criss-crossed, steep, winding, and unpredictable. There are not only stone needles, stone thorns and stone flowers formed by condensation, but also traces left by groundwater erosion of the river bed and multiple sinkings, which have high scientific research value.