The sprawling headquarters of the Shingon Buddhist sect and residence of Koya-san's abbot, Kongobu-ji is a temple complex that spans nearly a millennium of Japanese Buddhist architecture. The main gate dates to 1593, the present main hall to the 19th century, and the newest annexe was built in 1984. Inside the Great Main Hall, ornate fusuma sliding screens by 17th-century Kano school masters depict landscapes and seasonal scenes with breathtaking precision. You'll also find Japan's largest rock garden — a sea of raked white gravel representing two dragons protecting the temple — in the inner courtyard.