Located within the Hida-Kisogawa Quasi-National Park, Oniiwa Park is renowned for its dramatic landscape of enormous and unusual granite rock formations. Sculpted by wind and rain over millions of years, these rocks create a striking contrast with the surrounding greenery. The park has been designated a Natural Monument of Japan.
Near the summit of Eboshiiwa Mountain, visitors may occasionally see a waterfall that appears only after heavy rainfall. The park is also famous for its autumn foliage and offers beautiful natural scenery throughout the year. Ancient legends add a sense of mystery to this remarkable destination.
Each season brings a different charm to Oniiwa Park. Cherry blossoms brighten the landscape in spring, azaleas bloom in early summer, and clear streams provide a refreshing atmosphere during summer. In autumn, the surrounding mountains are transformed by vibrant foliage, attracting many visitors.
The name “Oniiwa,” meaning “Ogre Rock,” comes from a legend dating back approximately 800 years. According to local tradition, an ogre-like figure named Seki no Taro lived among these rocky mountains and committed misdeeds against nearby residents and travelers.
The ogre was eventually defeated by Koketsu Gengo, who acted under the orders of Emperor Go-Shirakawa. The story has been passed down through generations and is remembered in the traditional verse, “How terrifying—the ogre pampas grass of Jizuki Village.”
Several locations associated with the legend can still be found in the area, including the Ogre’s Cave and the Ogre’s Burial Mound. These sites give the park a distinctive atmosphere and make it an intriguing destination for visitors interested in Japanese folklore and spiritual traditions.
One of the park’s former attractions was Iwaana Kuguri, a route that allowed visitors to squeeze through narrow gaps between rocks. The route is currently closed for safety reasons. However, the Oniiwa Tourism Association occasionally organizes special events that allow visitors to experience rock passageways on a limited basis throughout the year.
Near the mountain summit is a large rock split by a deep crack. Because it resembles the rock that Tanjiro Kamado, the protagonist of the popular manga and anime series Demon Slayer: Kimetsu no Yaiba, cuts in two during his training, Mitake Town has named it Oni no Ittōiwa (Demon-Slaying Rock).
Fans of the series may enjoy seeing this distinctive rock formation while exploring the park’s rugged landscape.
Near the park lies Oniiwa Onsen, a hot spring area known for its radium-rich mineral waters. Traditional Japanese inns line the area, creating a relaxing atmosphere, while restaurants and souvenir shops offer opportunities to enjoy local food and shopping.
According to local tradition, the hot spring was discovered by the Zen master Kōho Genkun after he encountered an injured white eagle. The mineral spring has traditionally been associated with benefits for conditions such as high blood pressure, although such health effects should not be regarded as medically established treatment.
After exploring the park’s impressive rock formations and scenic trails, visitors can unwind at the nearby hot springs and enjoy the peaceful atmosphere of this nature-rich destination.
松野湖は、鬼岩公園を登るとたどり着くダム湖（人造湖）です。昭和36年（1961年）に灌漑用ダムとして完成し、周辺を森林に囲まれた広さ3.4ha、貯水量332万t、周囲6.6kmの湖は、四季折々の美しさを水面に映し出します。
周辺には遊歩道が整備されており、松野湖を一周（8キロメートル）することができます。遊歩道からは、湖畔の自然や周辺の山々を眺めることができます。