Cheomseongdae

Cheomseongdae is a 7th - century observatory in Gyeongju , South Korea , built from stacked granite blocks forming a bottle - like shape . A square opening near the middle provides access , while a flat stone platform crowns the rounded construction .

The structure was built under Queen Seondeok , who ruled the Silla Kingdom in the 7th century and supported scientific inquiry . Astronomers used it for centuries to predict harvest times and calculate lunar phases .

The name combines Korean words meaning observing the heavens , reflecting how astronomers once climbed inside to track stars and seasonal patterns . Local families often bring children here to learn about traditional sky watching methods that guided farming and festivals .

The site sits near the National Museum , reachable on foot or by bicycle along marked paths . Visitors can view the tower from the outside ; the interior remains closed to protect the ancient stonework .

The number of stone layers matches the days in a lunar year , while the shape of the opening symbolizes the transition between earthly and celestial realms . Some researchers believe the alignment points toward certain constellations during solstices .