Secret onsen and mixed-gender baths: the hidden side of Japanese hot springs

There's a moment, during a trip to Japan, when the noise of the cities starts to weigh on you. After so many lights, crowded trains, and the sparkling shop windows of shopping in Tōkyō and shopping in Ōsaka, a desire for something quieter, slower, more real arises. That's when you start wanting to move to more remote areas, where you can find inns of wood blackened by time, steaming tubs among the trees, and waters that have flowed from the same spot for centuries. These are the places of onsen, where you don't go to "do something", but to stop. There are many famous ones, but there are just as many, if not more, secret ones: small hot springs immersed in nature, far from tourist routes, where Japan seems to breathe at a different pace.

What is an onsen and why look for the secret ones

An onsen is a natural hot spring, fed by mineral-rich waters that flow from Japan's volcanic subsoil, around which villages, traditional ryokan and entire local cultures tied to ritual bathing have grown up over the centuries.

However, not all tubs are onsen: under Japanese law, for a bath to be called that, it must contain water that comes exclusively from a natural source and that has certain chemical and thermal characteristics.

The most famous onsen, like those in Hakone or Beppu, are well organized, easily accessible and equipped with modern facilities. While ideal for a first approach to this world, they're often crowded. By contrast, onsen away from the major tourist routes are characterized by small family-run facilities, open-air tubs carved into rock, wooden baths overlooking rivers or forests. Here time seems to slow down, and the experience is more intimate, authentic, almost meditative. Often you won't find English menus or large hotel complexes, but you can enjoy a simple dinner, perhaps a bentō prepared with local ingredients, and sleep in a tatami room worlds away from the frenetic city capsule hotels.

5 secret onsen to visit in Japan

Every season has its charm, which is why the best time to go to Japan depends mostly on the kind of experience you're looking for. Spring and autumn win you over with the colors of cherry blossoms and momiji, summer with its festivals, and winter in Japan is a riot of snow and illuminations. And it's also the best time to go discovering secret onsen!

To reach many of these "out of the way" onsen, it's essential to be able to find your way around easily, check local bus schedules or read up-to-date reviews: that's why renting a Pocket Wifi is a smart choice. It will let you stay connected even in the most remote villages and discover hidden hot springs that don't appear in the usual guides.

Tsurunoyu Onsen (Nyūtō Onsen, Akita)

In the heart of the mountains of Akita, the Nyūtō hot spring complex is home to one of Japan's most evocative onsen: Tsurunoyu.

Its open-air tubs, surrounded by snow in winter and lush greenery in summer, look like they've stepped out of a ukiyo-e print. The dark wooden structures and thatched roofs give the place an archaic atmosphere.

Mixed-gender bathing is also practiced here, and the milky, sulfur-rich water is famous for its skin benefits. Getting there takes some patience, but the reward is a rare kind of silence.

Kurokawa Onsen (Kumamoto)

Hidden among the hills of Kyūshū, Kurokawa is a small hot spring village that has chosen to limit mass tourism while maintaining a strict traditional aesthetic. No neon signs or modern buildings: just small wooden bridges, lanterns and ryokan immersed in nature.

One peculiarity is the "onsen passport", which lets you try different tubs in a single day. Perfect for those who want to explore without hurry and enjoy a romantic, relaxed atmosphere.

Ginzan Onsen (Yamagata)

If you're looking for a place that seems to have come straight out of a novel, Ginzan Onsen is the answer.
This village, famous above all in winter when snow covers the roofs and the lanterns reflect in the river, offers small hot springs with Taishō-era architecture.

Although it has become more well-known in recent years, it remains less crowded than the big names and retains a special magic, especially at dusk, when the sound of flowing water accompanies the warm steam.

Shirahone Onsen (Nagano)

The name means "white bones", inspired by the milky color of its waters. Shirahone Onsen is located in the Japanese Alps and is perfect for those who love combining trekking and relaxation.

The waters, rich in calcium, are great for circulation and for recovering after long hikes. Many ryokan here have panoramic tubs with mountain views that offer an immersive experience that changes completely with the seasons.

Ibusuki Onsen (Kagoshima)

Here the experience is different: in Ibusuki you don't just soak in water, but also in hot volcanic sand. You're literally buried up to your neck while the natural heat relaxes your muscles and stimulates circulation. A surprising experience, little known outside Japan, that combines hot-spring bathing with an ancient ritual. After the bath, nothing beats a dinner of fresh fish and local produce.

Onsen etiquette

Entering an onsen isn't just about taking a hot bath: it's a ritual with precise rules, born out of respect for others and for the water itself.

First of all, you wash thoroughly while sitting on small stools, using the showers and soaps provided. Only afterward do you enter the tub, without a swimsuit: nudity is natural and free of embarrassment.

It's forbidden to bring towels into the water (they're kept at the edge or folded on your head), you don't swim or make noise, and you try to maintain quiet, relaxed behavior.

Tattoos, although increasingly accepted, can still be an issue in some traditional onsen: it's worth checking in advance or covering them with special patches.

Mixed-gender baths: what they are and what to expect

Among these hidden onsen a nearly vanished tradition also survives: that of mixed-gender baths, called konyoku. Onsen generally separate women and men into different tubs, while in konyoku everyone shares the same hot spring water without embarrassment, naturally.

The atmosphere is generally respectful and calm, far from any Western idea of "transgression", although unlike regular onsen, a small towel or light garment is often required, though not always.

Either way, entering a mixed bath means accepting a different dimension of the body and of social interaction: here nudity isn't erotic, but natural, and sharing the hot spring space becomes an act of mutual trust. For many travelers it's one of the most memorable moments of their stay in Japan, precisely because it breaks stereotypes and brings them closer to an ancient tradition.

Once very common, they've now become rare and are often limited to traditional, remote locations like Tsurunoyu. Below are other locations famous for konyoku.

Shima Onsen (Gunma)

A historic hot spring town in the mountains north of Tokyo, Shima Onsen has several ryokan with mixed tubs, often open-air and overlooking the river. The atmosphere is very calm and not very touristy, ideal for those seeking authenticity without straying too far from the capital.

Okuhida Onsenkyō (Gifu)

A cluster of small hot spring villages in the Japanese Alps, famous for its mixed rotenburō (open-air tubs). Here you can soak in steaming water while looking at snow-capped peaks: one of the most iconic settings for this kind of experience.

Takaragawa Onsen (Gunma)

Perhaps one of the most famous konyoku, with huge natural tubs along the river. Despite being fairly well known, it remains a great example of traditional mixed bathing, with a relaxed, respectful atmosphere. Wearing a towel is often allowed, making it more accessible to foreign visitors too.

Kawayu Onsen (Wakayama)

Here hot water flows directly from the riverbed: by digging a hole in the sand you create an improvised, naturally mixed tub. It's one of the most "wild" and fascinating experiences you can have in Japan.

Myōjin Onsen (Nagano)

A remote onsen in the mountains, accessible only on foot or by bus, with simple, traditional tubs. Mixed bathing here is an integral part of local culture, and the surrounding silence makes the experience almost spiritual.

Sukayu Onsen (Aomori)

Famous for its giant wooden mixed tub (Hiba Sennin-buro), which can hold hundreds of people. Despite its size, the atmosphere remains surprisingly respectful and intimate.