By Air
Incheon International Airport, west of Seoul, is South Korea's main gateway and consistently ranks among the best airports in the world. It handles the great majority of international arrivals. Gimpo Airport, closer to central Seoul, handles some domestic flights and routes to Tokyo and Beijing.
Most major airlines fly into Incheon. Korean Air and Asiana are the two full-service national carriers; budget options include Air Busan, Jeju Air, and T'way Air for regional connections. From Europe, the flight takes around 11–12 hours; from the US west coast, around 10–11 hours.
From the airport, the AREX express train reaches Seoul Station in about 40 minutes (around 9,000 won). Slower all-stop AREX trains take 60 minutes but cost less than half the price. Airport limousine buses cover a wider range of destinations including suburban areas.
Busan has its own international airport (Gimhae), with direct flights from Japan, China, and Southeast Asia. If you are heading straight to the south of the country, flying into Busan rather than Seoul can save several hours.
By Sea
Regular ferries connect South Korea to China and Japan. From Japan, high-speed ferries run between Busan and Hakata (Fukuoka) in about three hours, and overnight ferries connect Busan to Osaka and Shimonoseki. From China, ferries operate from Incheon to Tianjin, Qingdao, Weihai, and several other ports — typically overnight crossings of 14–26 hours.
By Land
The only land border is with North Korea, which is not open to general travel. All overland entry is via the ferry and air routes above.