In the mountains of Nagano Prefecture, in a valley where the ground vents steam year-round, there is a hot spring pool surrounded by snow. In winter, Japanese macaques — 二ホンザル, nihonzaru — sit in it. Dozens of them. Shoulders deep in the water, faces relaxed, steam rising around them, snow falling on their heads.

The first time most people see a photograph of this they assume it is staged. It is not. The monkeys discovered the hot springs themselves, and they have been using them for decades.

How it started

地獄谷野猿公苑, Jigokudani Yaen-kōen — Jigokudani Monkey Park — sits in a valley in the Shiga Kogen area of Nagano. Jigokudani means "hell's valley," named for the steam that rises from the ground through the snow. Japanese macaques have lived in this region for a long time, but their use of the hot springs was first documented in the 1960s, when a young female monkey entered the outdoor pool at a nearby inn to retrieve dropped soybeans and discovered the warmth. Others followed. The behavior spread through the troop.

This is how cultural transmission works in primates: one individual does something, others observe and imitate, the behavior becomes established. The snow monkeys of Jigokudani did not inherit the knowledge of hot spring bathing. They invented it and passed it on.

What they actually do in there

The macaques use the hot spring exactly as you might expect. They soak during the coldest months — late November through early April — when the surrounding mountains are deep in snow. They groom each other in the water. Young ones play at the edges. The older animals sit with particular stillness, faces calm, eyes half-closed.

There is something unmistakably familiar about it. The posture of an animal in warm water is the same across species — a particular settling of the shoulders, a release of tension that is visible even from a distance. The monkeys look, as people have noted since the park opened to visitors, deeply at peace.

温泉 and Japan

That the snow monkeys found hot springs in Japan is not a coincidence. Japan sits on the Pacific Ring of Fire, with volcanic activity across most of the archipelago producing thousands of natural hot springs. 温泉, onsen, are woven into Japanese life at every level — neighborhood bathhouses, mountain resort towns, roadside stops, ryokan where the bath is the reason for the stay. Japan has more registered onsen than any other country.

The cultural significance of bathing in Japan runs deep: cleanliness, restoration, communal warmth. The monkeys of Jigokudani stumbled into a tradition that has been central to human life in this country for as long as anyone can remember. They recognized something good when they found it.

Visiting

Jigokudani Monkey Park is accessible from Nagano city, about two hours from Tokyo by shinkansen. The walk from the car park to the valley takes around thirty minutes through a forested path. The monkeys are present year-round but the winter months are when the bathing behavior is most consistent. There are no fences — the macaques are wild, and visitors walk among them. The park asks people not to touch the animals or make eye contact for too long. The monkeys largely ignore visitors, which makes the experience more remarkable rather than less.