Dewa Sanzan,
 
A "spiritual dive inside nature."

Dewa Sanzan 出羽三山 is the collective name given to the "Three Sacred Mountains of Dewa" — Mt. Haguro, Mt. Gassan, and Mt. Yudono. It has been a pilgrimage site for religious practitioners of ‘Shugendo’ for more than 1400 years. Shugendo 修験道 (in Japanese: "the Way of the Harsh Training”) is derived from Esoteric Buddhism practices; it includes principles from both the Shinto religion and Taoism and is strongly linked to Japan's original spirituality that centers on the worship of mountains. The practitioners of Shugendo are called Yamabushi 山伏 ("those who retreat in the mountains").
 
The Dewa Sanzan is one of the Three Main Sites of Shugendo in Japan (日本三大修験道), designated sacred in 593 by the legendary Prince Hachiko. In addition to being central for mountain-worshipping religious practices in the Tohoku region, the religious tensions between Mt. Yudono and Mt. Haguro led to the emergence of the Sokushinbutsu mummies phenomenon in the Shingon Buddhist temples of Mt. Yudono. Sokushinbutsu are mummies of Shingon Buddhist monks who committed to harsh practices in order to mummify their own bodies. This was done in an effort to become Buddhas themselves.The separation between Shinto and Buddhism—ordered by the Meiji Government in 1868—led to multiple transformations within Dewa Sanzan's Shugendo practice and its architecture.
 
Despite those transformations, Dewa Sanzan's practice of Shugendo has been continuous for the past 1400 years. Even today, you can attend Yamabushi rites performed by Yamabushi priests, and even interact with them.