Introduction to the pen-throwing trough: The pen-throwing trough is located between Tianshi Cave and Fanning Bridge. It was called the Longqiao Plank Road in ancient times. Below it is the pen-throwing trough, also known as the "pen-washing trough". The fissure is about 300 meters deep and 20 meters wide from the top of the rock to the bottom of the valley. The two rocks fractured to form a deep valley. In ancient times, wooden bridges were used to bridge the gap. Later, a dangerous half-wall passage was cut through the rock, with stone railings beside it. From here, you can see the red cliff above your head. Rock, overlooking the deep valley, the scenery is strange and dangerous.
According to the "True Shape Map of the Five Mountains" of the Han Dynasty: at the Dragon Bridge, there are overhanging rocks on both sides, overlooking unexpected events. There is a ghost oath stone beside the mountain. The heavenly master Zhang Daoling and the ghost soldiers swore an oath to order the devil not to harm the people again. The mountain was painted with red ink, the green cliffs were interrupted, and the handwriting became grooves, leaving a wonder.