Mamono no Kyōkoku (魔物の峡谷,Valley of Monsters) is a large area located within the land of demons. The Mamono no Kyōkoku is a large mountain forest, known to be home to great beast which became known as the Shinjū. Within the valley lies the Sekiseikon and the Inyō Izumi (陰陽泉,Yin-Yang Spring).