In sub-zero temperatures, a Japanese macaque monkey soaks in the warmth of a mountain hot spring at Jigokudani (Hell's Valley) in Nagano Province of central Japan. The Japanese macaques, also referred to as snow monkeys, live freely in this area that is covered by snow one third of the year. Jigokudani is the only known place in the world where monkeys bathe in natural hot springs. As a habit, they come down from the mountains where they spend the night and bathe during the day.