@tika_mits: One of my favourite things to see in Seoul - the Changing of the Guards ceremony at Gyeongbokgung Palace. It takes place right at the main gate (Gwanghwamun) and it's free to watch since it's outside the ticketed area. Held daily (except Tuesdays) at 10:00am and 2:00pm with each performance lasting about 20 minutes. No ticket needed unless you want to go into the palace afterwards.