Hwangudan was a Joseon-era altar complex where the Korean emperor performed the Rite of Heaven, a ceremony asserting Korea's sovereignty equal to China. The main altar was demolished by the Japanese colonial administration in 1913 and replaced by the Joseon Hotel (now the Westin Chosun). The surviving circular stone drum tower (Hwanggungu) stands on the hotel grounds, incongruously surrounded by luxury hotel architecture.
The tower is small but interesting — an octagonal stone structure with intricate carvings, one of the few physical traces of the brief Korean Empire. It can be seen from the street through the hotel grounds and is sometimes accessible for closer inspection. The site is within walking distance of City Hall and makes a worthwhile stop when exploring the Myeongdong area.