Originally built in 1483, Changgyeonggung Palace (창경궁) is one of the five grand palaces of the Joseon Dynasty. According to the Korea Tourism Organization, it often served as residential quarters for queens and concubines. During Japanese colonial rule, a zoo and botanical garden were placed on the palace grounds. The zoo was removed in 1983, but the botanical garden remains.
Among the attractions inside the palace grounds are the small but historic Okcheongyo Bridge (옥천교) built in 1483, Myeongjeongjeon Main Hall (명정전), and the living quarters of the royals who lived there.
Three of the more odd things that you can see in the palace are an ancient observatory that looks like a set of stairs built in 1688 called Gwancheondae (관천대), an octagonal 7-storied stone pagoda that was built in 1470 in China and bought from an antique dealer, and a shrine for the placenta and umbilical cords of King Seongjong (성종태실 및 태실비). In addition to these, built during Japanese colonial rule, a beautiful greenhouse still exists within the palace grounds.
Sitting at my desk and looking back, I cannot recommend visiting Changgyeonggung Palace to anyone but those who have the time and determination to see everything Korea has to offer in terms of historical sites. The adjacent Changdeokgung Palace UNESCO World Cultural Heritage site has more to see and will be a better use of time for a traveler on a tight schedule.