Located in Gongju-si, Gongsanseong Fortress is a mountain castle which was established during the Baekje Period (234-678). The castle is about 2.5km long, and there are two ways of touring the castle. One way is to start from the parking lot, pass the west gate, Geumseoru, and walk along the cement road. The other way is to turn left at the beginning of the cement road and walk along the top of the castle, which is called Sanseong Road. The cement road is very smooth and you can walk along it comfortably. On the other hand, Sanseong Road has many twists and the passage is narrow, but it has the advantage of following along the Geumgang riverside.
About a 45min bus ride from the Yuseoung Bus Terminal (2 min walk from Guam Subway Station) , easy to walk around, take pretty pictures, and even try your hand at a bit of archery :)
*Very easy day trip, and the bus trip from Daejeon was only W2300...so very affordable! Definatley worth a look.*