Panmunjeom — Many tour companies offer DMZ tours which is a day trip from Seoul, the highlight of which is a village lying in the Demilitarized Zone between North and South Korea. Note that you cannot visit without booking with a tour company, and that some nationalities including South Korean and Chinese are not allowed to visit for seccurity reasons.
Yeongjong Island — Beaches, hot springs and fresh sea breezes.
Incheon — The place where U.S. Gen. Douglas MacArthur landed in the Korean War; it also has the biggest and oldest Chinatown in Korea.
Gapyeong — Popular weekend getaway, east of Seoul. A small town in the mountains of Gyeonggi-do, on the border of Gangwon-do.
Chuncheon — Filmed in many Korean dramas and movies and now accessible by subway from Seoul
Suwon — One of Seoul's satellite cities, located 30 kilometers south of Seoul, the city is best-known as the home of Hwaseong Fortress íì±, a UNESCO world heritage site. Built from 1794 to 1796, the fortress consists of four main gates and a 5.76 kilometer-long wall, and features an archery range and other activities. Suwon is also famous for its local football club Suwon Samsung Bluewings as well as galbi with numerous restaurants serving the dish. And also you could go to " Folk village " from there. Suwon has several stops on Seoul Subway Line 1 and is about an hour away from Seoul Station. Several commuter trains travel from Seoul Station to Suwon Station each day, with the trip taking about 30 minutes.
Busan Take the KTX down to Busan to enjoy the beach in summer. Makes a nice change of pace from Seoul.