Hongseong is a county town in South Chungcheong, inland enough to feel agricultural but close enough to the Yellow Sea to smell of seafood at the right tables. It is not polished like Korea's better-known heritage towns, but it has a useful mix of hill walks, old walls, and working west-coast ports.
The best single sight is Yongbongsan Mountain, a low ridge with more rock and view than its height suggests. Inland, Hongju Eupseong Fortress gives the town its historical centre. On the coast, Namdang Port is the place to come for prawns, cockles, and a look at the tidal flats.
Hongseong is best for travellers already moving through Chungcheong rather than a first Korea trip. Give it a day if you want a mountain walk, a seafood meal, and a county-town version of Korea that does not feel staged for tour buses.