The Jigokudani Yaen-koen (altitude 850 meters) is located in the Valley of Yokoyu River sourced from Shiga-Kogen of the
Joshinetsu-Kogen National Park in northern part of Nagano prefecture.
Because of the very steep cliffs and the steam coming off the springs in everywhere, ancient people called this valley ‘Jigokudani (Hell valley)’ .
Also it is buried in snow almost one third of the year. Even that kind of severe environment here is a paradise on earth for monkeys to live in.
The troops of wild Japanese macaque (they are popularly known as snow monkeys) inhabit here naturally through the ages.
Since the establishment of Jigokudani Yaen-koen in 1964, it has been a worldwide popular place for watching the bathing
monkeys in a hot spring and for ecological observation of researchers or photographers,
and some of them who visited here have accomplished certain results in the area.