Changdokkung Palace (The Secret Garden) ★★★
It was built in 1405 by King Taejong and neighboring with Changgyong Palace. Inside theChangdokkung Palace, the Secret Garden is the best known place, composed of 78 acres of beautifuloriental plant life, with pavilions, ponds and wooded areas. In ancient times, only royal familymembers were allowed to go in for pleasure, so it has been known as the Secret Garden.
Only guided tour 
(English tours are 11:30, 13:30 & 15:30 and Japanese tours are 10:30, 12:30 &14:30).
Each tour lasts for about 70 minutes.
Open: 09:15-17:30 (closed every Monday)
Admission fee: adult 2,200 won/ children 1,100 won
Information: (02)762-8262
How to go: about 300m East from exit #3, Anguk station(18) on Orange #3 line 

Changgyong Palace ★★
This is the oldest and one of the largest royal palaces in existence today. Built by King Sejong in1419, it was used by the Japanese during the Japanese colonial rule as a zoo but fully restored in1986.
Open: 9:00-16:30 (closed every Monday)
Admission fee: adult 700 won/ free for children
Information: (02)762-4868 (in Korean)
How to go: about 800m Southwest from Hyehwa station(20) on Blue #4 line 

Jongmyo Shrine 
This Royal Shrine was first established in 1395, soon after Chosun Dynasty founder King Teajo established his capital in Seoul. It houses the spirit tablets of the king and queens of the Choson Dynasty, and once a year a memorial service is still held at the shrine by the descendants of theroyal Yi family. It has recently been added to UNESCO's list of World Heritage Sites.
Open: 9:00-19:00 (closed every Tuesday)
Admission fee: adult 700 won/ children 300 won
Information: (02)762-8263
How to go: exit #3, Jongno 3-ga station(53) on Red #1 line 

Gyeongbokgung Palace ★★
Built in 1395 by King Taejo, this is the protype of the ancient palace from the Choson Dynasty (1392~1910), and was designated the official residence of the royal family. Traditional indigenous life styles and customs can be seen in The National Folk Museum which is located at the North part.
Open: 09:00-18:00 (Mar. thru Oct.), 09:00-17:00 (Nov. thru Feb.) (closed every Tuesday)
Admission fee: adult 700 won/ children 300 won
Information: (02)732-1931 (in Korean)
How to go: exit #5, Gyeongbokgung station(17) on Orange #3 line 

Gyeonghi Palace 
Closed to the Sejong Cultural Center, this palace was commissioned by King Gwanghae in 1617 and called Gyeongdokgung until 1760, when King Yeongjo renamed it Gyeonghigung. The Seoul Municipal Museum of Art is within the compound. Admission inside the royal residence under construction is not permitted. 
Open: daily 24 hours 
Admission fee: free
Information: (02)739-8971 (in Korean)
How to go: about 200m Northeast from exit #4, Seodaemun station(532) on Purple #5 line 

Deoksu Palace ★★
Located in the heart of the downtown Seoul across from City Hall, it is a popular stop for tourists aswell as city dwellers who enjoy the stroll through the grounds. Deoksu Palace boasts the first Western style building, Seokjojeon, which is presently being used as the Royal Artifact Museum. In addition, the royal guards changing ceremony is being held here from 14:00 to 15:30 on every Sat. & Sun. (Apr.06 thru Nov. 01)
Open: 9:00-19:00 (closed every Monday)
Admission fee: adult 700 won/ children 300 won
Information: (02)319-8809 (in Korean)
How to go: about 50m South from exit #2, City Hall station(1) on Red #1 line