Flight
Seoul has two main airports, but for most international flights you'll find that they fly into ICN. There are airport limousine buses that depart every 20 minutes (which I find the most convenient going into downtown Seoul) or a subway line that connects the airport directly to Seoul. If you will be bringing large heavy bags, I'd recommend hopping on the limousine bus or taking a taxi. Again, I recommend the limousine bus since the stop announcements will be in English and they go to most places in Seoul.