Cheomseongdae is an ancient astronomical observatory located in Gyeongju, South Korea. Built during the Silla Dynasty in the 7th century, it is one of the oldest surviving observatories in East Asia. The structure is made of 362 granite stones, symbolizing the days of the year, and stands about 9 meters tall. The design of Cheomseongdae features a cylindrical base and a square top, reflecting the ancient Korean belief in the harmony between heaven and earth. It was used to observe celestial bodies and track time, playing a crucial role in the development of astronomy in Korea.