An onsen (温泉) is a term for hot springs in the Japanese language, though the term is often used to describe the bathing facilities and inns around the hot springs. Onsen come in many types and shapes, including outdoor (露天風呂 or 野天風呂 roten-buro or noten-buro) and indoor baths.
Jigokudani Monkey Park (地獄谷野猿公苑 Jigokudani Yaen Kōen) is in Yamanouchi, Shimotakai District, Nagano Prefecture, Japan. The name Jigokudani, meaning “Hell’s Valley”, is due to the steam and boiling water that bubbles out of small crevices in the frozen ground, surrounded by steep cliffs and formidably cold and hostile forests. It is famous for its large population of wild Japanese Macaques (Macaca fuscata), more commonly referred to as Snow Monkeys, that go to the valley during the winter, foraging elsewhere in the national park during the warmer months.
The Japanese macaque (Macaca fuscata), historically known as saru (“monkey”), but now known as Nihonzaru (Nihon “Japan” + saru) to distinguish it from other primates, is a terrestrial Old World monkey species native to Japan. It is also sometimes known as the snow monkey from the fact that it lives in areas where snow covers the ground for months each year—no primate, with the exception of humans, is more northern-living, nor lives in a colder climate.