Seoul

By ship
By ship

There are ferry services to various points in China from the neighboring port city of Incheon. Currently no services run from Japan directly to Seoul; many Koreans take the coach or KTX train to Busan, where several ferry and hydrofoil options are available.

By car
By car

No matter where in Korea you start your journey, there will be tolled expressways Gosok Doro and national highways Gook Do that lead to Seoul; the most important one is the Gyeongbu Expressway, linking Seoul with Busan. To avoid the daily traffic jam on the Gyeongbu Highway near Seoul, take Jungbu/2nd Jungbu, Seohaean, or Yongin-Seoul Expressway.

By train
By train

Seoul is the northern terminus of the KTX high-speed line. There are three KTX stations within city limits:

Seoul Station
서울역 for trains to Busan, Ulsan, Kyeongju, Daegu, Daejeon Cheonan/Asan, and Suwon. Accessible via subway lines 1 & 4.
Yongsan Station
용산역, for trains to Mokpo, Gwangju, Daejeon and Cheonan/Asan. Also on line 1 & 4 Sinyongsan Station.

The newly added KTX at Youngdeungpo is now running to southern destinations.

Nearly all ordinary non-KTX services also use one or both of the above terminals, but services east to Chuncheon or Gangneung and southeast to Gyeongju via Danyang use Cheongnyangni Station 청량리역, to the east of the city on line 1.

By bus
By bus

Every weekend approximately 2 million Seoulites leave the city, which goes a long way to explaining why the city has five major intercity bus terminals.

Central City Terminal
also known as Honam Terminal, Metro Lines 3, 7 or 9, Express Bus Terminal stn. Directly adjacent to the Express terminal, serves buses to North and South Jeolla.
Dong Seoul Bus Terminal
동서울버스터미널, Gangbyeon stn Line 2. Buses to points east of Seoul Gangwon and some part of North Chungcheong.
Seoul Express Bus Terminal
서울고속버스터미널, Metro Lines 3, 7, or 9, Express Bus Terminal stn. Also known as Gangnam Terminal and Gyeongbu-Yeongdong Terminal, this is the largest of them all and serves pretty much the entire country, but most services head east incl. Busan, Daegu, Daejeon. Lines to Jeolla, however, use the Central City/Honam Terminal right next door. For the most part there's no need to buy a ticket days in advance except for maybe during holidays. There's even a ticket window labeled "Tickets for Foreigners" where the attendant can speak English. Fare from Seoul-Busan is about ₩20,000 and buses come continuously throughout the day. Small restaurants and snacks are all throughout the station. Journeys longer than 2 hrs. typically will have a short stop at a rest area. Most buses are very comfortable and extremely safe.
Nambu Bus Terminal
Nambu Bus Terminal stn Line 3. Serves places southwest of Seoul Southern Gyeonggi, South Chungcheong and nothern North Jeolla.
Sinchon Bus Terminal
Sinchon Underground stn Line 2 or Sinchon stn Gyeongeui Line. Buses to Ganghwa Island. Note: That's Sinchon station, not Sincheon, which is also on Line 2 but on the wrong side of the city!