Gyeongbokgung Palace (경복궁) , Korea is located in busy Seoul. It is a wonderfully preserved (and rebuilt) palace originally built centuries ago. During certain times they have traditional colourful Korean military guards with swords and halberds, guarding the decorative Gwanghwamun gate.
It has free entry during the summer month of July, but is inexpensive at other times, and is open mostly all year round, with one or two days of particular Korean significance.
Wikipedia says;
Gyeongbokgung (경복궁/景福宫), also known as Gyeongbokgung Palace or Gyeongbok Palace, was the main royal palace of the Joseon dynasty. Built in 1395, it is located in northern Seoul, South Korea. The largest of the Five Grand Palaces built by the Joseon dynasty, Gyeongbokgung served as the home of Kings of the Joseon dynasty, the Kings’ households, as well as the government of Joseon.
Gyeongbokgung continued to serve as the main palace of the Joseon dynasty until the premises were destroyed by fire during the Imjin War and abandoned for two centuries. However in the 19th century, all of the palace’s 7,700 rooms were later restored under the leadership of Prince Regent Heungseon during the reign of King Gojong. Some 500 buildings were restored on a site of over 40 hectares.[1] The architectural principles of ancient Korea were incorporated into the tradition and appearance of the Joseon royal court.
In the early 20th century, much of the palace was systematically destroyed by Imperial Japan. Since then, the walled palace complex is gradually being reconstructed to its original form. Today, the palace is arguably regarded as being the most beautiful and grandest of all five palaces. It also houses the National Palace Museum of Korea and the National Folk Museum within the premises of the complex.
The official webpage can be found here.