Introduction to the Cliff Corridor: Guoliangdong is the first tunnel across the cliff in South Taihang. It is known as the father of the Taihang Tunnel. It is 1250 meters long, 6 meters wide and 4 meters high. The 35 windows on the outside of the corridor were originally used to quickly clear debris and provide ventilation and light. Now these skylights have become observation decks for enjoying the scenery. To dig this tunnel, 4,000 8-pound hammers were used to break the tunnel, and 12 tons of steel drills were consumed. During the construction process, 13 young warriors hammered, drilled and blasted, and the blasted debris was cleaned up by men, women and children in the village. It was praised by foreign friends as "the eighth wonder of the world".