Konyoku: Mixed Bathing

Four large rotenburo (outdoor baths) line the banks of the Takaragawa River here, surrounded by forest and, in winter, deep snow. The baths are mixed-bathing (konyoku), and yuami-gi bathing wraps are provided so anyone can join comfortably. There is also a women-only rotenburo for those who prefer privacy, plus an indoor bath. The inn opened in 1923, and arriving here still feels like stepping into a different world: the wooden buildings, the sound of the river, the steam rising off the water. The walk between baths along the riverside is part of the pleasure.

The oldest inn in the Nyuto Onsen cluster, Tsurunoyu sits at the end of a forest road under thatched roofs that have been here for centuries. The signature mixed rotenburo flows with milky-white sulfurous water, opaque enough that you can barely see below the surface, which makes mixed bathing feel natural and easy. Women enter through their own changing area and step straight into the shared bath. Four pools in total, including an indoor bath. The water smells of sulfur, the milky colour comes from fine mineral particles in suspension, and in winter the contrast of white water and white snow is quietly stunning.

Awanoyu sits in the Shirahone valley of the Japanese Alps, and the water here is what draws people: milky-white and faintly carbonated, rich in calcium and magnesium bicarbonate, with a bottom you cannot see. The big mixed outdoor bath (konyoku rotenburo) is the heart of the place: women enter from a separate changing room, walking in while already submerged, and thick bath towels keep things comfortable. The inn itself dates to 1912, classic wooden construction set in national park forest, and the sulfurous smell hits you before you even step off the bus.

The sennin-buro ("thousand-person bath") at Sukayu is a vast, cavernous hall built entirely from hiba cypress, a wood with natural antibacterial properties and a warm, resinous scent. The hall has been here for about 300 years, and stepping inside still feels like entering another era: low light filtering through the steam, the smell of sulfur, the sound of water. It is a mixed bath (konyoku), and a rental yuami-gi wrap is available for those who want one. Women have two dedicated women-only periods each day (8-9am and 8-9pm). The water is highly acidic and sulfurous, so keep metal jewelry off, as the reviews note it tarnishes quickly.

The senninburo at Kanaya Ryokan is, by common account, the largest all-hinoki (cypress) bath in Japan. Built in 1915 (Taisho 4), the vast wooden hall stretches roughly 20 metres and bathes you in the clean, warm scent of cypress throughout. It is a mixed bath (konyoku): women can also enter a connected women's bath and benefit from women-only hours. The ryokan itself was established in 1867 in Izu, Shizuoka, tucked in a quiet valley with spring water flowing directly from the base of Kanaya Mountain. Beyond the great hall, there is also a small outdoor rotenburo for those who want open sky. The combination of hot spring water, cypress, and a 160-year-old inn is genuinely hard to find elsewhere.

The Hosokan bath at Hoshi Onsen Chojukan is a high-ceilinged Meiji-era wooden hall that looks much as it did when it was built in the 1880s. Its most unusual quality is that the spring water rises visibly through the pebble floor of the bath, so you can watch it bubble up from below. The bath is mixed (konyoku), and the atmosphere tends to be peaceful; nobody seems to pay much attention to anyone else. The inn has been here for about 150 years, set in forest beside a small mountain river, and the sense of time standing still is genuine. There is also a women's indoor bath and a rotenburo for other times.

Kita Onsen has been a working ryokan since at least the Edo period, and the building barely seems to have changed: rough wooden floors, low ceilings, a Tengu mask watching over the entrance. The spring itself has reportedly been known for over 1,200 years. There are five distinct baths: a riverside rotenburo, a large outdoor pool (the kind with a small slide, which gives a sense of the relaxed spirit of the place), and several indoor ones including the women's bath upstairs with its window wall looking out onto greenery. Most of the outdoor baths are mixed (konyoku) or open to men and women at different times. It became briefly famous abroad as a filming location for the film Thermae Romae.

Aoni Onsen is one of those places that earns its reputation by refusing to modernise: no in-room electricity, no cell signal, no Wi-Fi. At night, a staff member brings an oil lamp to your room, and the only light you have is that flame. The four bath facilities are scattered across the property: indoor wooden baths, a waterfall-view bath (Takimi-no-yu), and an open-air mixed rotenburo (konyoku) beside the mountain stream. The waters themselves are clear and mild. Getting here requires a special shuttle bus in winter, which adds to the sense of arriving somewhere genuinely remote.

The spring at Zao is among the most acidic in Japan: the water sits around pH 1.3 to 1.6, and it turns a striking milky bluish-white as it hits the air. Zenshichi-no-yu draws directly from this source with 100% kakenagashi (free-flow, no recycling). The main bath is mixed (konyoku) for most of the day, with women-only hours in the afternoon (3-6pm) and swimsuits required outside those hours. There are also private baths for those who want them. The inn sits in Zao Onsen village, one of the major onsen resort areas in the Tohoku region, with a long history going back to a legendary spring discovery around 110 CE.

Motoyu is a small open-air rock bath tucked at the base of Momiji Bridge in the steamy gorge town of Tsuetate Onsen, right at the edge of the Tsuetate River. The water is clear chloride spring water, hot at the source but diluted to a comfortable temperature. Large rocks provide natural screening, and despite being a fully open konyoku bath beside a public path, reviews note it is considerably more approachable than it looks. Local legend traces this spring back over 1,800 years to Empress Jingu, who supposedly used it as a birth bath. The surrounding gorge town, famous for its carp-streamer festival, is itself atmospheric, with steam rising from the streets.

Each winter, between December and February, the stony bed of the Otaigawa River at Kawayu Onsen (Wakayama) is excavated to create a vast open-air communal bath called the Senninburo ("Immortals' Bath"). Hot spring water at 73 degrees Celsius seeps up naturally from below and cools to bathing temperature where it mixes with the river. The scale changes every year depending on conditions, and the edges you dig yourself define your spot. Swimsuits and towels are required here: this is a riverbed, public and wide open, and the rules exist accordingly. The name suits it: lying back in the water under a winter sky, the place feels genuinely otherworldly.

Fukiage is a free, unstaffed wild bath (noyu) in the forest near Tokachidake in Hokkaido, reached on a short walk from the nearest parking. There are two pools fed by the same source: the lower one sits around 44 degrees Celsius and is perfectly usable, while the upper pool runs close to 50 degrees and is mostly for the brave. The water is clear and odourless, a sodium-calcium chloride type flowing straight through without treatment. There are no changing rooms. The setting is pure forest, and after a long soak the walk back through the cold air feels part of the experience. Became briefly famous through the TV drama "Kita no Kuni Kara" (From the Northern Land).