It takes 20 minutes to drive from southern Seoul to Suwon, which is on the Seoul subway line. From Suwon, it’s an easy 30-minute drive to areas on the Yellow Sea. To go to Chay-boo Island, on the Korean western seaboard, it will be about a 45 min. bus ride from Suwon train station (tides permitting!).
Also, the city of Suwon has invested great time and cash into the “restoration” of places-of-interest in Suwon. Kudos to them for transforming some run down areas into beautifully restored/added-to/created palaces and monuments.
Do beware: the locals drive dangerously!
Have fun!