Cheom-seong-dae(lit. 'star-gazing tower') is an astronomical observatory in Gyeongju, South Korea. Cheomseongdae is the oldest surviving astronomical observatory in Asia, and possibly even the world. It was constructed in the 7th century(under the reign of Queen Seondeok, year 632~647) in the kingdom of Silla, whose capital was Seorabeol, or present-day Gyeongju.
Cheomseongdae stands 9.17 meters high and consists of three parts: a stylobate, or base upon which a column is constructed, a curved cylindrical body, and a square top. Midway up the body stands a square window and entrance to the inside of the structure. The square stylobate base is 5.7 meters wide and built from a single layer of 12 rectangular stones. From the base to the window, the tower is filled with earth and rubble. The cylindrical body of the tower is built out of 365 pieces of cut granite, symbolizing the number of days in a year. (source: wikipedia)