The Three Mountains of Dewa, also known as Dewa Sanzan in Japanese, are three special mountains in the ancient Dewa Province of Yamagata Prefecture. The three mountains are Mount Haguro, Mount Gassan, and Mount Yudono. These mountains are considered sacred in the Shinto religion and are particularly significant for the Shugendo mountain ascetic cult. Many people, including the well-known haiku poet Matsuo Bashō, visit Dewa Sanzan as a popular pilgrimage site.