The main headquarters of Koyasan Shingon-shu is located at Koyasan (Mount Koya) in Wakayama prefecture, Japan. In an environment filled with spiritual feeling, the main pagoda towers among the great cryptomeria and cypress trees. This is a sacred place unparalleled in the world, and is filled with the power and grace of Kobo Daishi whom we look upon as the founder of Shingon Buddhism. Kongobu-ji, the name of the main headquarters temple, was given by Kobo Daishi as the general name for the mountain temple.
Here is a well put article in Conde Nast Traveler “The Magic Mountain” April 2007.