Wonsando is the island side of Boryeong, reached from the mainland coast and worth considering when Daecheon feels too built up. The appeal is low-key: fishing villages, sea views, beaches, and a slower look at the same Yellow Sea landscape that the city sells in festival form.
It is best with your own wheels or a clear transport plan. Treat it as a half-day coastal detour rather than a quick central-city sight.