Mount Koya is the mountain on which Kukai (Kobo Daishi)
established the headquarters of the Shingon
school of Mikkyo Buddhism
In 816, ten years after he returned from China, the Emperor granted Kobo Daishi Mt. Koya (Koyasan) as a place to found a monastic center. He had asked the Emperor for this land because he needed a location remote from the capital (remote in those days when travel meant walking) where monks could practice meditation without distractions. He lived there off and on from 818 until his death in 835.
Koyasan remains the headquarters of the main branch of Shingon Buddhism. It's only a little over an hour from Osaka by express train. Many people come just to see the artistic and architectural beauties of the temples. Others come to experience Shingon ceremonies while staying at the temples, many of which accept guests for overnight stays or longer. Some temples accept visitors who don't speak Japanese.
The temples are built on a generally flat tableland in the Yoshino mountains at an elevation of 800 meters (2600 feet). The temples are laid out as a mandala, with a great pagoda in the center, the Daito. The tower houses a central statue of Dainichi Nyorai surrounded by statues of other Buddhas and paintings representing Bodhisattvas. This mandala, like the painted mandalas found on the walls of all Shingon temples, is a symbolic representation of reality. Just as a priest in meditation may "enter" a visualized mandala to venerate the Buddhas and Bodhisattvas depicted on it, priests and laypeople can visit Koyasan and enter the mandala.
Many of the buildings are open to visitors, including the museum, home to some of Japan's greatest treasures of religious art.
There are also a great many shops and merchants selling junky trinkets.