Unjusanseong Fortress (운주산성, also known as ‘Gosansanseong Fortress’) is a cultural heritage of the Baekje Dynasty. This is a mountain fortress built along the surrounding three mountain peaks in the westernmost and southernmost parts of Mt. Unjusan (460m in elevation). The fortress, which borders 3 villages in Jeondong-myeon and 2 villages in Jeonui-myeon, consists of a 3,098m-long outer fortress wall and 543m-long inner fortress wall. Both the outer and inner fortress walls are built with stone. Considering the number of formerly inhabited sites that have been unearthed, it is obvious that there were many buildings in the fortress and the surrounding hills. In the fortress, many broken pieces of earthenware from the Baekje period, porcelain from the Goryeo and Joseon periods, and broken tile from the Baekje, Goryeo and Joseon periods have been discovered. Mountain trails have been improved for family hikers. The mountain peak has a great view of the Independence Hall of Korea, Asan Bay, and the downtown areas of Cheonan and Cheongju. It takes about 2 hours to reach the peak.