Step back in time at Gyeongbokgung Palace, the grandest of Seoul's five royal palaces. You can easily spend a few hours wandering through the vast grounds, exploring the intricate architecture of the throne halls and royal quarters. Don't miss the Royal Guard Changing Ceremony at the main Gwanghwamun Gate at 10am and 2pm! The self-service ticketing machines open at 9am, so I'd recommend lining up at 8:50am if you'd like to experience the peace and quiet of the grounds.
For a cultural experience and free entry, you can rent a traditional 'hanbok' from a nearby shop before you go in. Locals appreciate it as long as you are respectful!