When you arrive at Incheon, head to the basement to get on the airport railroad to Gimpo. Make sure you get the commuter train that stops at stations instead of the express one that goes straight to Seoul Station. Alternatively, you can take airport limo 600 to Gimpo. The journey on the train to Gimpo is around 30 mins.
Gimpo At International Airport Station, transfer to subway line 9. Take a subway to a Youido Station and go to exit 5 and walk for five minutes. We are located on the 8th floor in Manhatan building (Yeouido department store).