Changdeok-kung (kung/gung is Korean for 'castle' or 'palace') has a lot of different names; with Biwon (The Secret Garden in English) probably being the most common. Though calling it Biwon might get you a lecture on that being the Japanese name for the place and hence not its 'real' name, it's still what most people call it.

Unlike nearly all the other palaces in Korea, Changdok/Changdeok Palace can only be seen as part of a tour. There are Korean language tours on the hour from 9 a.m. to 5 p.m. plus English tours at (usually) 11:30, 1:30 and 3:30. The English tours are generally a lot less crowded and take about 90 minutes. Tours in other languages can be arranged as well.

Hours: First tour (in Korean) leaves at 9 a.m. and the last tour (also in Korean) leaves at 5 p.m. Closed on Mondays!

Transportation
Subway: get off at the orange line's (line three) Ankuk Station and the walk will be 5-10 minutes
Taxi: tell the driver 'Biwon' or 'Chang-dawk-kung'

Directions: Follow the maps from the subway and exit heading east. The palace is on the north side of the road about five minutes from the station.

Website: http://www.cdg.go.kr/