As many as 200 snow monkeys live in the proximity of Yudanaka Onsen, one of a string of onsen villages in the mountainous north of Nagano Prefecture.
In winter they take dips into a rotemburo, an activity that they are said to have first started in the 1960s when a local ryokan keeper left food out for them during the cold months by a hot pool. A special pool was subsequently created especially for the macaques and they can be watched frolicking and soaking themselves in the piping-hot water.
There are also simian-free onsen in and around the village, if you prefer to do your bathing unaccompanied by monkeys. These are a great place to spend a few indulgent hours in steaming, soothing and bubbling waters.