Mount Osore (恐山, Osore-zan) is the name of a Buddhist temple and folk religion pilgrimage destination in the center of remote Shimokita Peninsula of Aomori Prefecture, in the northern Tōhoku region of northern Japan. The temple is located in the caldera of an active volcano and is believed in Japanese mythology to be one of the gates to the underworld.
The mountain is the location of a Sōtō Zen Buddhist temple, Bodai-ji (菩提寺), 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.
A unique feature of Bodai-ji is the presence of mediums known as itako who claim to summon the souls of the dead and deliver messages in their voices. These mediums were traditionally blind and had to receive extensive spiritual training and purification rituals; however, in modern times their number has dwindled and not all are blind. The temple has a twice-yearly Itako Taisai festival held in summer and autumn.
The temple also maintains a hot spring resort for use by pilgrims and tourists.