Originally Posted by
guwinster
There is an express commuter rail style subway that runs from both Incheon and Gimpo Airports to Seoul Station. Seoul Station is maybe a 5-10 minute walk from the Millennium Hilton. The subway costs something like 3-3.50 USD. If you get disoriented at Seoul Station, a taxi from Seoul Station to the hotel would be another 3 USD (the base fare).
The express train to ICN costs about 7 USD, leaves every 30-40 minutes and is takes 43 minutes and does not stop at Gimpo. The local train costs 3-4 USD, leaves every 10-15 minutes and takes 56 minutes. While you absolutely have to take the express train if you check-in at Seoul Station if you're not checking in there then the only advantage is the slightly shorter ride, better seats and less people. This means the express train is virtually empty all the time because only 4 airlines have check-in desks at Seoul Station.