Introduction to Shimen: Baogu Shimen is a natural museum. Since the Spring and Autumn Period and the Warring States Period, this has been the hub of communication between the Central Plains, northwest and southwest. The plank road erected on the "difficult to reach the sky" Shu Road can be called a miracle of ancient transportation, and the stone gate is the most dangerous and strange part of the plank road. Now the newly built antique plank road is flying on the steep cliff, tracing the vicissitudes of history. During the Eastern Han Dynasty, the Shimen Tunnel was excavated using the method of "fire and water stimulation" and was the earliest artificial tunnel opened to traffic in the world.