Chungcheong Suyeongseong Fortress in Boryeong is a stone fortress built by the Joseon dynasty (1392-1897) in the 16th century to defend against invasions through the Hwanghae Sea. It offers a picturesque view of the Hwanghae Sea and several islands. The entrance to the fortress, called Manghwamun Gate, showcases stone artistry with its polished granite arch. This site also has historical significance as a place where Catholic persecution occurred in the 19th century.