Introduction to Cavern Valley: There is a karst canyon downstream of Huangyanggou. The water flowing down from Huangyanggou passes through the underground river in the canyon. When traveling at the bottom of the valley, you can only hear "Woo" coming from underground. The sound of "Woo" makes people feel that the underground is like a huge corridor, mysterious and unpredictable, hence the name of Cavern Valley.