Located 2,789 feet (850 meters) above sea level in the Valley of Yokoyu, Jigokudani Monkey Park stands out as one of Japan's most popular and unique onsen. Although onsen (the Japanese term for hot springs) are popular throughout the country, the ones in the frequently snow-covered region of Joshinetsu-Kogen National Park in Northern Nagano attract more than just human bathers.
The forests of the valley serve as the natural habitat of wild Japanese macaques, or snow monkeys, who gather in large groups to bathe in the natural hot spring water. Jigokudani Monkey Park features a man-made onsen where the natural hot water collects and the monkeys congregate, making it possible to view and photograph these wild animals from a safe distance. Visitors are not allowed to bathe with the monkeys but can choose to visit one of the area's human-centric onsen to do some soaking of their own.
Monkey sightings are not guaranteed, but the best time to see them is during the snowiest months of the year, typically from December to March. In warmer months, the monkeys may still be around (sometimes with babies in tow), but they don't enter the pools as frequently.