Wongudan Altar, located in Jung-gu, Seoul, South Korea, was built in 1897 to serve as a site for the performance of the rite of heaven. The site was also known by other names, such as Hwangudan (환구단, 圜丘壇), Jecheondan (제천단, 祭天壇) and Wondan (원단, 圜壇). Wongudan was designated South Korea's Historic Site No.