Jigokudani (Hell Valley) Monkey Park is an incredible natural wonder in Yamanouchi, Nagano Prefecture, Japan! It is a part of the Joshinetsu Kogen National Park and located in the valley of the Yokoyu River. Its name is derived from the steam and boiling water that come from the crevices of the frozen ground in the region, which resemble an underworld landscape amongst the steep cliffs and hostile forests!