Deoksugung Palace served as the main palace of the Great Han Empire.
Be sure to catch the Royal Changing of the Guards Ceremony being held at the Daehanmun Gate. Schedule is 11:00, 14:00 and 15:30. This is held outsiide the gate so it's free.
The palace opens at 9 am and closes at 9 pm. It is CLOSED on Mondays.
Admission Fee is KRW 1,000 for adults and KRW 500 for children
But if you plan to visit all the major palaces, better avail of the Combination Ticket for Palaces.