Cheomseongdae is an important historical place in Gyeongju, South Korea. It is believed to be the oldest surviving astronomical observatory in Asia, built around 632 AD during the reign of Queen Seondeok of Silla. The observatory has a circular structure with stones laid in the shape of a half-moon. It is said to have been used for calculating the lunar calendar. It is also thought to have been used for studying stars, astrology and meteorology. The observatory is considered an essential part of Gyeongju's history and culture and a popular tourist attraction. Cheomseongdae has been designated as a UNESCO World Heritage Site since 2000, along with the Historic Monuments and Sites in Gyeongju. It stands as a testament to the advanced astronomical knowledge of the Silla people and is a must-see for any history enthusiast visiting South Korea.