Sanzu River
The mountain is the location of a Sōtō Zen Buddhist temple, , which claims to have been founded in 862 AD by the famed monk Ennin, with Jizō Bosatsu as its main image. The temple was abandoned in 1457 and restored back to use in 1530. In popular folk religion, the otherworldly setting of Mount Osore, with its charred landscape of blasted rocks filled with bubbling pits noted for unearthly hues and noxious fumes came to be one of several places in Japan identified to be an entrance to the Underworld. A small brook running to the neighboring Lake Usori was equated to the Sanzu River, a river that deceased souls need to cross on their way to the afterlife.