보은 삼년산성

Boeun Samnyeon Sanseong (Boeun Three-Year Mountain Fortress) is a Silla-period mountain fortress in Boeun, Chungcheongbuk-do, named after the recorded tradition that the fortress took three years to build. Originally constructed in the late-5th century during the reign of Silla king Jabi, the fortress is one of Korea's earliest and most architecturally significant Silla-period stone-fortress sites, designated as Historic Site of South Korea. The fortress walls run approximately 1.7 km around the hilltop, with stone-built walls reaching up to 22 m in height in places, and the surrounding valley landscape that gives the fortress its strategic-defensive context. Walking the fortress walls provides both archaeological-and-historical insight and panoramic views back across the Boeun-area landscape. Pairs naturally with broader Boeun-area itineraries including Sokrisan and Beopjusa.