Japanese 'snow monkeys' walking around a hot spring (onsen) in Jigokudani ('Hell's Valley') in the mountains of Nagano prefecture northwest of Tokyo. These Japanese macaques (Macata fuscata fuscata) gained international fame through their habit of bathing in a local hot spring (onsen) in the depths of winter. Known as nihonzaru in Japanese, they are in fact able to endure temperatures as low as minus 10 degrees Celsius, but learned the habit from human bathers in the nearby country inn (ryokan ).