Cheonan is an easy day trip south of Seoul, close enough on the KTX to feel suburban but with a stronger identity than most commuter towns. It is best known for Korean independence history: the huge Independence Hall of Korea sits east of town, while the Yu Gwan-sun sites in Byeongcheon keep the March 1st independence movement close to the surface.
The city itself is spread out and practical, with malls, universities, bus terminals, and apartment blocks, but there are good reasons to leave the station area. Gakwonsa Temple climbs into the foothills of Taejosan, the Arario complex brings contemporary art into the middle of the bus-terminal district, and Byeongcheon Sundae Street turns a local blood-sausage specialty into a small food pilgrimage.
Cheonan works best if you pick two or three targets rather than trying to love the whole city. Start with the Independence Hall, add Gakwonsa or the Yu Gwan-sun memorial, and finish with sundae in Byeongcheon if you want the day to feel properly local.