Acha-san (316m & 287m) and its higher but less-famous sibling Yongma-san (348m) are three
sibling peaks only 600m apart, forming the southeastern end of the Bukhan-san Sub-Range of
north-of-the river Seoul City (right on the border with Gyeonggi-do's Guri City). They overlook
the Han River as it enters Seoul from the east, and thus an observation-post/ fortress was
long established on those peaks, giving them a "guardian" character. Five Buddhist temples
and a few Shamanic shrines are found on their steep slopes, and the Sheraton Walker Hill
Hotel (one of Korea's leading 5-star tourism complexes) is on the south face.