The spring town is the largest natural spring in France, ranked fifth in the world, and the annual flow of spring water is 630 million cubic meters. Geologists infer that there should be a large groundwater system under this spring, which accumulated more than 100 kilometers away from Fengdu Mountain. Snow melt water and rain on the peace day Water. Second, how deep this spring is, people have not figured out yet. From the 19th century to the present, there are 16 deep spring explorations recorded, each result is different, and with the development of detection technology, detection instruments are more compact, people can always find this spring deeper than everyone thinks. In 1989, the detection instrument reached 308 meters, but the cave was too narrow to continue .