The so-called 'snow monkeys' of Japan, congregating around a hot spring (onsen) in Jigokudani ('Hell's Valley') in the mountains of Nagano prefecture northwest of Tokyo, gained international fame through their habit of bathing in the depths of winter. These Japanese macaque s (Macata fuscata fuscata), known as nihonzaru in Japanese, 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 )..