Located in Gongju-si, Gongsanseong Fortress is a mountain castle which was established during the Baekje Period (234-678). The fortress is more than 2.6 kilometers long at 110 meters above sea level. Built using earthen fortifications during the Baekje dynasty, the fortress was strengthened during the Joseon dynasty with stones. There are many structures and relics left from the Baekje, Goryeo, and Joseon dynasties within the fortress. At the West and East entrances, visitors can enjoy a thick forest with the Geumgang River in the background. It is worth the visit for its historical and cultural significance, and also for the beautiful view of the Geumgang riverside and the walking trail.