Cheomseongdae observatory was constructed during the empire of Queen Seondeok (r. 632-647). It's one of the oldest astronomical observatory in the world. The observatory consist of 365 stones, symbolizing the number of days in a year. The rocks are piled in 27 layers symbolizing the 27th ruler, Queen Seondeok, and the days in a lunar month by adding the two rock layers on top.
Unesco: Gyeongju Historic Areas
RR: 10x10 RR
Date: Feb 25