One of the Korea palace tour attractions that you can find near Seoul City Hall.
It use to be used as the royal palace in emergency times but as the time went by, after the royal palace was built, it was more used by other royal family members. More detailed information is explained on the official web page.
Address :
서울시 중구 세종대로 99 덕수궁
Seoul Junggu Saejongdaero 99 Deoksugung
Cost :
Normally costs 1,000 KRW,
but if wearing Korean traditional dress (Han-bok) you can enter for free.