Originally Posted by
stargold
You get access to priority security on departure if you've used the City Air Terminal in COEX. You can do the passport control there too, and you just show the stamped passport at ICN in the diplomat/APEC lane.
Can you also do this at the Seoul Station, taking the express train to the airport? The times I have been on the (regular) airport train, they advertise that you can check in, check baggage, and passport control all at the rail station. I wasn't sure if this was for every airline/flight/destination.