The Sauna Boom in Japan: Cold Plunges and Outdoor Saunas

Why Japan fell in love with the sauna, what the cold plunge adds, and where visitors can sweat beside a lake, a river or the sea.

Published October 26, 2026 at 9:53 AM JST | By Tokyo Paul

Quick answer: Japan's sauna boom is built on a simple loop: heat in the sauna, a short dip in a cold bath called mizuburo, then a rest that leaves many people feeling "totonou," or pleasantly reset. A 2024 industry survey estimated about 17.8 million sauna enthusiasts, and visitors can try the loop at public bathhouses, onsen, dedicated sauna facilities and outdoor tent saunas.

Few trends have changed everyday Japanese leisure as quickly as saunas. Once seen as a corner of the bathhouse for tired office workers, the sauna became a lifestyle through manga, social media and a new vocabulary of relaxation. Visitors now ask where to try it, what the cold plunge is for, and how outdoor saunas work. This guide explains the boom, the sauna, plunge and rest routine, the places to go, and the etiquette that keeps shared baths pleasant for everyone.

How the Third Sauna Boom Began

Japan's present enthusiasm is usually described as its third sauna boom. According to the Ministry of Foreign Affairs' Web Japan magazine, the first wave started after a dry sauna heated by a steam pipe was installed at a Ginza bathhouse called Tokyo Onsen in 1957. Finnish athletes then brought sauna equipment to the athletes' village for the 1964 Tokyo Olympics, and press coverage helped spread the idea nationwide.

The second boom came in the 1970s and 1980s with "spa lands," large leisure complexes that combined baths, saunas, massage and restaurants for the whole family. Because those venues offered separate men's and women's saunas, they also helped bring women into sauna culture, which had been mostly a men's pastime in earlier city saunas.

The current boom took off in the late 2010s and gathered pace after the pandemic years. Web Japan credits the manga Sado, or "The Way of the Sauna," by Katsuki Tanaka, and a bestselling book on sauna technique with turning the sauna into something young adults in their twenties and thirties talk about openly. The word that came with it is totonou, a verb for the refreshed, clear-headed feeling that follows the full cycle.

The Sauna, Plunge and Rest Cycle

The routine behind totonou has three steps that repeat. First comes time in the sauna room, then a quick plunge in cold water, and finally a rest on a chair or bench in the open air or a quiet room. Many facilities post the suggested timing, and one English-language guide published in 2025 describes about six to twelve minutes in the heat, roughly thirty seconds to a minute in the cold bath, and five to ten minutes of rest with a drink.

Japanese saunas often run as dry, hot rooms heated by electric stoves or stones, with a clock on the wall so bathers can track their own time. Some rooms add steam. Löyly, the Finnish word for the burst of steam made by ladling water over hot stones, has become part of the vocabulary, and some venues offer aufguss, where an attendant fans the steam through the room with a towel.

Everyone responds differently to heat, so the best habit is to follow the posted rules, drink water before and after, and leave the room whenever it feels like too much. Anyone with a heart condition, high blood pressure or other health concerns should ask their doctor before trying a hot and cold routine.

The Numbers Behind the Boom

Hard figures show how large the sauna world has become. The Japan Sauna Institute's 2024 survey, based on an internet poll of 10,000 adults aged 18 to 69 in March 2024, estimated that Japan had about 17.79 million sauna enthusiasts in 2023, up from 16.81 million the year before. Those counted here include light users who go at least once a year, medium users at least monthly and heavy users at least four times a month.

The same report found that the rise came from light users, whose number grew to roughly 11.3 million, while the groups who go most often had not yet returned to their 2020 level. In other words, the sauna is welcoming a wide new audience of casual visitors, which is good news for first-timers who worry the scene is only for experts.

On the supply side, Japan's health ministry surveyed roughly 13,000 sauna facilities nationwide in a review reported by Jiji Press in April 2026. The survey looked at practical safety equipment such as emergency call buttons, so it is worth noticing where the button is when you settle in.

Mizuburo: Understanding the Cold Plunge

Mizuburo literally means "water bath," and in sauna culture it is the cold plunge that follows the heat. Facilities usually offer one or more tubs, often between about nine and twenty degrees Celsius, and a few have several tubs at different temperatures. A Time Out Tokyo guide from February 2026, for example, describes one Tokyo venue with two cold baths at 16 and 9 degrees and another with three plunges set to different temperatures.

The etiquette is straightforward. Rinse off your sweat before getting in, enter slowly so the cold does not come as a shock, and keep your head out of the water, submerging only up to the neck. Many people stay under a minute. Some facilities have a shower or a slightly warmer pool for beginners, and a few outdoor tubs let the cold air do part of the work.

After the plunge, dry off before sitting on rest chairs, because shared furniture is expected to stay dry. That small courtesy is one of the most visible rules in sauna facilities across the country.

Sento, Onsen and Dedicated Sauna Facilities

The easiest place to try the sauna is a sento, the neighborhood public bathhouse. The Tokyo Metropolitan Government's visitor news site reports that roughly 430 sento remained in the city as of December 2024, according to the Tokyo Sento Association. Many include a sauna room, and the association says sauna popularity among young people has increased bathhouse use because sento can offer a similar experience for less than standalone saunas.

Onsen, or hot spring resorts, often add saunas to their baths, and many ryokan now advertise a sauna and a cold plunge in the same breath as their hot spring water. A newly opened example is KAI Miyajima, a hot spring ryokan from Hoshino Resorts, which in July 2026 announced a stone sauna called ishiburo based on a Kamakura period tradition, heated by radiant warmth at about fifty degrees.

Dedicated sauna facilities in big cities lean toward design, with themed rooms, multiple plunge pools and quiet rest areas. Prices vary widely, so check the facility's own site for entry fees, towel rental and whether reservations are needed.

Outdoor Saunas by Lakes, Rivers and Sea

Outdoor saunas are the part of the boom that most appeals to travelers. Web Japan describes tent saunas heated by wood-burning stoves stacked with sauna stones, where bathers can sweat surrounded by nature and then cool off in the sea, a river or a lake instead of a cold tub. The tents are portable, which helps explain why they appear at campsites, riverbanks and lakeside resorts.

In 2025, one travel guide listed examples including private tent saunas in Saitama, a Kyoto operator offering a river plunge and, in winter, snow dips, and a Nagano guesthouse with forest cabin saunas beside groundwater plunges and nearby Lake Nojiri. At glamping resorts, tent saunas are increasingly part of the stay. Glamp Village Setouchi Shimanami in Hiroshima Prefecture announced in June 2026 a private tent sauna plan for one group a day with a self-löyly style and firewood included, so first-timers can join.

The practical rules for outdoor saunas are the same as indoors: follow the operator's instructions, watch the water conditions for any lake, river or sea plunge, and never go in alone if the water is deep or fast.

Etiquette and Practical Tips for Visitors

Most saunas in Japan are gender-separated, and nudity is expected in the bathing areas. Where mixed groups are allowed, swimsuits or sauna wear are normally required, and some venues provide robes. Bring a small towel, shower thoroughly before entering, and avoid dripping through changing rooms. Many sauna rooms discourage loud chatting, and some post a no-talking rule.

Tattoos are handled differently from place to place. According to Time Out Tokyo's 2026 guide, some venues welcome them, some require a cover and at least one does not allow entry, so check the facility's rules before you go. Sento are generally more relaxed than onsen, based on the Tokyo Sento Association's comments.

Bring water, avoid going when you feel unwell, and skip alcohol before using the sauna. Lockers are usually coin-return or key-based, so carry a few coins. Peak hours are evenings and weekends, so mornings are often calmer for first-timers.

Why the Sauna Fits Japanese Bathing Culture

The sauna feels familiar in Japan because bathing was already a social, restorative ritual. Sento, onsen and ryokan baths taught generations of people to wash first, soak, rest and talk quietly. The sauna and cold plunge add contrast to the same idea. For many visitors, a sauna session is an easy way to enjoy bath culture without the pressure of a long onsen trip.

Wellness also plays a role. The boom coincided with a wider interest in sleep, stress relief and time away from screens, and Japanese sauna fans often describe the quiet of the rest period as the real prize. That makes the sauna a gentle companion to hiking, cycling or a hot spring town stay.

Anyone planning a trip can mix a neighborhood sento in the city with a ryokan sauna in the countryside, and finish with an outdoor tent sauna beside a lake if the season is right.

Want to go deeper? Tokyo Paul's book Onsen Towns is available on Amazon.

Frequently Asked Questions

What does totonou mean in a Japanese sauna?

Totonou is a Japanese verb used by sauna fans for the refreshed, calm feeling that follows a full cycle of sauna heat, a cold plunge and a rest. It literally relates to being put in order. Web Japan notes that the idea is especially popular with people in their twenties and thirties.

Do visitors need to be nude to use a sauna in Japan?

In most gender-separated saunas and sento, nudity is expected, with a small towel for modesty on the way to the bath. Mixed or outdoor saunas normally require swimwear or sauna wear. Rules differ by venue, so read the posted guidance or ask staff before you go in.

Are cold plunges safe for everyone?

Cold water puts stress on the body, and the sauna and plunge combination is not suited to everyone. Facilities suggest short plunges, entering slowly and listening to your body. People with heart or blood pressure concerns, pregnant visitors and anyone unsure should ask a doctor first and follow each facility's posted rules.

Keep Exploring

More guides from Tokyo Paul: Onsen Etiquette Step by Step: Bathing the Japanese Way, Onsen with Tattoos: A Friendly Guide to Hot Springs in Japan and Higaeri Onsen: A Hot-Spring Day Trip From Tokyo.