Onigajo is the one of the national scenic beauties and natural monuments of Japan.
The legend said, in the time of Emperor Kanmu (early 9th century), the general Sakanoue no Tamuramaro marched this area to conquest the pirates here. The head of pirates was called Ogre. Sakanoue no Tamuramaro defeated the pirates and later, this rock was named under his legend.
This site is registered as The UNESCO World Heritage Site, "Sacred Sites and Pilgrimage Routes in the Kii Mountain Range."