Take the Airport Railroad (AREX) Express or All-Stop train to Seoul Station (direct & reliable). If you have heavy luggage, consider an airport limo bus or taxi.
Try tteokbokki, gyeranbbang and grilled skewers along Myeongdong’s stalls — iconic first-night introduction to Korean street food and great for photos.
See the colorful Changing of the Guard and walk through the palace grounds; winter light is crisp for photos. Palace entry is cheap but Hanjeong (dress rental for photos) is popular.
Full guided DMZ tour (Dora Observatory, 3rd Infiltration Tunnel, Dorasan Station). Tours run mornings and return late afternoon; ID and passport required for some tours (JSA requires extra clearance).