First settled in 819 by the monk Kūkai, Mt. Kōya is primarily known as the world headquarters of the Kōyasan Shingon sect of Japanese Buddhism. Located in an 800 m high valley amid the eight peaks of the mountain (which was the reason this location was selected, in that the terrain is supposed to resemble a lotus plant), the original monastery has grown into the town of Kōya, featuring a university dedicated to religious studies and 120 temples, many of which offer lodging to pilgrims. The mountain is home to the following famous sites:
Okunoin (奥の院), the mausoleum of Kūkai, surrounded by an immense graveyard (the largest in Japan)
Danjogaran (壇上伽藍), a heartland of Mt. Kōya.
Konpon Daitō (根本大塔), a pagoda that according to Shingon doctrine represents the central point of a mandala covering not only Mt. Kōya but all of Japan
Kongōbu-ji (金剛峯寺), the head temple of the Kōyasan Shingon Buddhism
Kōyasan chōishi-michi, the traditional route up the mountain
It also houses a replica of the Nestorian stele
In 2004, UNESCO designated Mt. Kōya, along with two other locations on the Kii Peninsula, Yoshino and Omine; and Kumano Sanzan, as World Heritage Sites "Sacred Sites and Pilgrimage Routes in the Kii Mountain Range".