The Kaesong Chomsongdae Observatory is an astronomical observatory from the period of Koryo Kingdom which is situated in the west of Manwoltae in Kaesong Municipality.
In view of its present position and the records of the History of Koryo, the observatory is believed to have been built in the early period of Koryo, when the Yongyong Palace was being built on Manwoltae. Now there remains only its granite platform. Originally, there were astronomical observation instruments on the platform.
The plane of the platform was square and the platform consisted of stone pillars and stone floors laid on the pillars. The platform is 2.8 metres high and each side of it is 2.6 metres long. The pillar stones number five, four standing at the four corners and one in the middle. The sides of the platform face the cardinal points. It was constructed accurately and solidly.
From the early period of its foundation Koryo had national agencies in charge of astronomical and meteorological observation to do relevant observation at astronomical observatories and record the results meticulously. The records of sunspots observed from 1105 to the closing years of Koryo number over 150.
The Kaesong Chomsongdae Observatory is a valuable legacy showing the state of astronomical observation and high architecture of Korea at that time.