Located near City Hall station, Daehanmun Gate is the main gate of Deoksugung Palace, one of the princiapl five palaces of Joseon dynasty. The name "Daehan" means wish for eternal prosperity of the Korean Empire. In front of the gate, the Palace Royal Guard Changing Ceremony is held twice daily, along with the reproduction of costumes and style throughout the year.
Source: Korea Tourism Organization official English tourism database. Opening hours and details can change — check the official website before visiting.