How long does it take to get to downtown Seoul from Inchon International Airport?
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Taking Airport Railroad would be the best way to get to Seoul from Incheon airport.
There are two types of Airport Railroad, express train and all-stop one.
If you take all-stop train from Incheon airport, it will take about 52 min to arrive at Hongik University station (Hongdae), and an hour to get to Seoul station. It would cost you 4,150 krw(4$).
Express train would take you to Seoul station in 43 min. It will not stop at Hongik University station since it's an express one. The cost would be 9,500 krw(9$).