Deoksugung palace or 덕수궁 located in the centre of Seoul, not far from main royal palace Gyeongbokgung. But also Gyeonghuigung palace is near.
Entrance fee is 1,000 Won and the palace is opened from 9 a.m. to 9 p.m.
Also you can see the change of the toyal guards daily at 11 a.m. , 2 p.m. , 3.30 p.m.
Deoksugung was built during the mid-1400s and became a prince Wolsan residence. But now every single person can visit this place :-)
Palace area is not too big but beautiful. You can see the palace, former living houses... Of course Gyeongbokgung palace is the biggest one and you should firstly visit it, but Deoksugung palace area is quite and adorable so I also recommend you to visit it :-)