Koyasan is a sacred mountain located in Wakayama Prefecture, Japan. It is the center of Shingon Buddhism, founded by the monk Kōbō Daishi in the 9th century. The area is home to over 100 temples, including the famous Okunoin, which houses the mausoleum of Kōbō Daishi. Visitors to Koyasan can experience its serene atmosphere, beautiful landscapes, and traditional temple lodging known as shukubo. The mountain is also a UNESCO World Heritage Site, recognized for its cultural significance and historical importance in Japanese spirituality and religion.