Introduction to the coupon cave: There is a coupon cave in the south wall of the second-floor platform of Zhenbeitai. The inner masonry steps lead directly to the third floor. The coupon cave is inscribed with the word "Xiang Ming" on the banner, and "Zhenbeitai" is inscribed on the north side (now destroyed). ), both were written by Tu Zongjun, governor of Yansui during the Wanli period. The three characters "Zhenbeitai" were inscribed by the contemporary calligrapher Wei Tradition.