When Flying Beats the Train
On the Korean mainland, the KTX high-speed rail network wins almost every domestic routing decision once you count real door-to-door time: city-center-to-city-center stations beat an airport-to-airport flight after you add the trip to the airport, security, and the transfer from the arrival airport into your destination city. The clear exception is Jeju Island, which has no bridge or rail link to the mainland — flying, or the ferry described below, is the only way to reach it directly, and the main Jeju air route is also the busiest in the country by a wide margin. Beyond Jeju, flying mainland-to-mainland (Seoul–Busan, Seoul–Daegu, and similar) rarely saves meaningful time or money over the KTX, and it adds two airport transfers instead of one.
Gimpo (GMP): Seoul's Domestic Airport
Gimpo International Airport (GMP), in Gangseo-gu on Seoul's west side, is the city's domestic hub, separate from Incheon, which handles nearly all international traffic. Gimpo's own site confirms it is reachable by subway lines 5 and 9 and the Airport Railroad (AREX), all serving Gimpo Airport Station, connected to the domestic terminal's western ground floor; by intercity bus routes 11-1, 11-2, 11-3, and 11-4 from the domestic terminal's west side; and by taxi from stands outside gates 6 and 8, reached via a pedestrian bridge. Domestic check-in and security windows are set by each airline, but Gimpo's own guidance is that domestic check-in typically closes around 30 minutes before departure — build in a margin beyond that, and confirm your specific airline's cutoff when you book.
The Gimpo–Jeju Route
The Gimpo–Jeju corridor is Gimpo's marquee domestic route and is frequently cited as one of the busiest air routes in the world by passenger volume — a product of Jeju having no fixed link to the mainland and very heavy domestic tourist demand. In practice that means extremely high flight frequency, with departures in both directions every few minutes at peak times, but it also means the route sells out around Korean holidays — Seollal (Lunar New Year) and Chuseok — and on summer weekends, so book ahead for those windows rather than assuming a same-day seat will be waiting.
Jeju and the Other Regional Airports
Jeju International Airport (CJU) is, unsurprisingly, extremely well connected: its own site confirms domestic service to Gimpo (Seoul), Busan, Daegu, Gwangju, Ulsan, Yeosu, Pohang-Gyeongju, Sacheon, Gunsan, Yangyang, Cheongju, Muan, and Wonju — direct flights from Jeju reach nearly every regional airport in the country. Ground transport at the terminal includes city and intercity buses (Gate 2), taxis (Gate 3), limousine buses (Gate 5), and a dedicated rental-car shuttle to an off-terminal "rental car house."
Korea's other regional airports, each confirmed operating via its own official page:
- Gimhae/Busan (PUS) — the country's second-busiest airport, handling domestic routes alongside a smaller slate of international ones; reachable by the Busan–Gimhae light rail at Gate 1 or by bus at Gate 4.
- Daegu (TAE) — domestic connections to Seoul/Gimpo, Busan/Gimhae, Jeju, Cheongju, Muan, Yangyang, Gwangju, Ulsan, Yeosu, Pohang-Gyeongju, Sacheon, Gunsan, and Wonju.
- Cheongju (CJJ) — operates both domestic and international flights, though I could not confirm its specific route list from the official page I could load.
- Yangyang (YNY), serving Gangwon province — its own site noted, at the time I checked, that international bookings were unavailable "due to airline circumstances," so treat YNY as effectively domestic-focused for now and check current status before planning an international leg through it.
- Muan (MWX) — domestic routes to Seoul/Gimpo, Busan/Gimhae, Jeju, Daegu, Gwangju, and Ulsan among others, alongside some international service.
All of these airports, plus Gimpo and Jeju, are operated by the state-run Korea Airports Corporation (KAC), which lists 14 airports nationwide under one customer service line (1661-2626, 06:00–23:00 daily).
Domestic Carriers and Fares
Official airport pages for Gimhae and Yangyang confirm the following carriers actively operating on Korean domestic routes: Korean Air, Asiana, Jeju Air, Air Busan, Air Seoul, and Jin Air. Korean Air and Asiana are the full-service legacy carriers; the rest are low-cost carriers that typically undercut them on fare, especially when booked weeks ahead. I was not able to confirm current fare levels from an official source in this research. As a general pattern, domestic fares in Korea are inexpensive by international standards if you book early, and rise sharply for last-minute bookings and for travel around Seollal and Chuseok, when a large share of the country is moving and Jeju-bound seats in particular sell out. If your trip touches either holiday period, book your domestic flight as early as you can.
The Domestic Terminal Routine
Domestic flying in Korea is fast. You don't clear a passport-control queue the way you would internationally, but as a foreign traveler you should still carry your passport as photo ID at check-in and security — a home-country driver's licence isn't guaranteed to be accepted as identification the way it would be for a Korean domestic-only traveler. Several airports (Gimhae, Cheongju among them) display live security wait-time information on their own sites, which suggests queues are generally short and closely monitored. Airline domestic check-in windows close around 30 minutes before departure per Gimpo's own guidance, so arriving 45–60 minutes ahead of a domestic flight is normally comfortable — confirm your specific airline's cutoff when you book.
Baggage on Low-Cost Carriers
Korea's low-cost carriers (Jeju Air, Air Busan, Air Seoul, Jin Air) generally follow the standard LCC pattern of a modest included cabin-bag allowance with checked baggage sold as a paid add-on, but I was not able to confirm current specific weight limits or fees from an official source in this research. Check the exact allowance on your booking confirmation or the airline's own baggage page before you pack — LCC baggage fees paid at the airport counter are typically far higher than the same allowance booked online in advance.
Connecting From Incheon to Gimpo
If you're arriving internationally at Incheon (ICN) and connecting to a domestic flight from Gimpo, you're moving between two separate airports, not two terminals of one. Incheon's own site confirms it publishes public-transport guidance covering buses, trains (AREX), and taxis, but I could not retrieve the specific route or timing details for the Incheon-to-Gimpo leg itself from the pages I was able to load. As a planning rule of thumb, budget at least 2 hours between an international arrival at Incheon and a domestic departure from Gimpo, to clear immigration and customs, transfer between the two airports, and get through domestic check-in and security — more if you're arriving at a peak time or unfamiliar with the route. Confirm the fastest current option (an AREX connection, an airport limousine bus, or a taxi) and its timing directly with Incheon Airport's own transportation information before booking a tight connection.
The Ferry Alternative
For travelers bringing a car, uneasy about flying, or just after a slower arrival, ferries to Jeju run from mainland ports including Mokpo, Wando, and Busan. I was not able to load a working page in this research confirming current routes, operators, crossing times, or fares, so treat this as a real option worth researching rather than a confirmed itinerary — check current schedules directly with Jeju's tourism authority or the ferry operators before booking, since car-carrying ferry routes and timetables shift seasonally.