Introduction to the Hollow Watchtower: The place where the Great Wall and the Yellow River intersect is called Laoniu Bay, located in Pianguan County, Shanxi Province. This was a castle for stationing troops during the Ming Dynasty and was built in the third year of Chenghua (AD 1467). On the cliff close to the Yellow River in Laoniuwan Fort, there is a brick hollow watchtower that is still well preserved. This tower stands majestically on the cliff, overlooking the Yellow River. It is one of the famous scenic spots in Pianguan.