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What is a Japanese Onsen?

There’s arguably no better Japanese tradition than soaking in an onsen. And if you’re travelling to Japan, visiting an onsen should be on your to-do list. But what is an onsen? What are the rules? And how do you find them? Read on for a quick primer on Japanese hot springs.

A brief history of the Japanese onsen

Japan is a nation of volcanoes – and therefore, a nation of hot springs. And with nearly 2,300 “onsen towns” and 25,000 hot spring sources, Japan has plenty to choose from.

To the ancient Japanese, onsens may have been created by the gods, but legends abound about the country’s hot springs being discovered by animals. The most notable of these is Dogo Onsen in Matsuyama, Ehime.

Dating back 3,000 years, Dogo Onsen is officially Japan’s oldest onsen. It is mentioned in Japan’s oldest texts and was a favourite spot of celebrated novelist Natsume Sōseki. Legend has it that locals discovered the onsen after observing an egret’s daily flight to heal its injured leg with a soak in its therapeutic spring waters.

There are even onsens, like the famous Jigokudani Yaen-Koen (Jigokudani Monkey Park), exclusively for animals! (But visitors will find an inn and hot spring for humans just down the mountain.)

A private outdoor onsen steaming and surrounded by snow.
Kashikiri at Naruko Onsen, Miyagi Prefecture

The health benefits of onsens

That egret of lore at Dogo Onsen was in fact partaking in toji (湯治, hot water healing). Balneotherapy – treating maladies by soaking in natural mineral water – is practiced around the world and goes back at least to the days of Cleopatra.

Fed by natural springs, onsens vary greatly in what they offer. It’s common to see info posted about the hot spring, such as the water’s temperature, mineral content, pH level and the health benefits it provides.

To best benefit from the curative powers of an onsen, it’s said you should stay at least 2 to 3 nights at the onsen to convalesce and let your body fully absorb the host spring’s minerals.

What’s the difference between a sento and an onsen?

A sento is a Japanese public bath

A sento (銭湯) is a public bathhouse not fed by a natural hot spring. They’re typically found in residential areas and easily identified by a nonren curtain hanging in the doorway with ゆ (yu, meaning hot water) on it. They have separate bathing areas for men and women.

An onsen is a Japanese hot spring

Onsen (温泉) literally means warm (温) spring (泉), and the word is used to refer both to the bath itself and the surrounding hot spring area. To be legally deemed an onsen, the water must be over 25 °C and meet specific mineral requirements outlined in a law called the “Hot Springs Act”.

Most onsens range between 39 ℃ and 42 ℃ (102-107.5 °F) but can be much hotter. Yumura Onsen in Hyogo – Japan’s hottest hot spring – reaches a scorching 98 ℃ (208.4 °F)!

Types of onsens

There are various types of onsens, with indoor (内湯, uchiyu) and outdoor (roten-buro, 露天風呂) baths being what you’ll encounter most often. Less common are notenburo, or yatenburo (野天風呂), which are open-air baths typically in remote locations with no amenities.

Mineral-wise, there are 19 different types of onsens, including Sulphur for treating arthritis, iron for anemia, and alkaline, hydrogen, and sulfate to name a few.

There are plenty of public onsens in Japan and some are within a day trip from Tokyo. However, many onsens are in hotels or ryokans (traditional Japanese inns) and only open to registered guests.

Ryokans have one large common bath (大浴場, daiyokujo) open to all, and possibly smaller private baths called kashikiri (貸切). These can be reserved for a specific time (often for an hour at a time) or even be attached to your room – for your own private onsen for your entire stay!

Do onsens have mixed-gender bathing?

This is something to keep in mind when planning your travel, especially if you want to enjoy the onsen experience with your significant other.

Most onsens have separate bathing areas for men and women. But you can still find mixed-gender onsens – called konyoku (混浴) – in Japan. Although, you won’t find any mixed onsens in Tokyo, as they’re banned in the nation’s capital.

Most konyoku nowadays require bathers to wear swimwear, but there are still mixed onsens where you need to be naked.

Do you have to take your clothes off at an onsen?

Yes. (Well, probably.) Most onsens require bathers to be naked. As noted above, mixed onsens are the typical exception to this rule, although some make you take it all off.

Men sitting in an outdoor shared onsen in the winter, surrounded by snow.
Roten-buro at Tsurunoyu Onsen, Akita Prefecture

Where are the most popular onsens?

With so many onsens, choosing where to go can be challenging. It also depends on the season, for some onsens, such as Tsurunoyu Onsen in Akita, are best experienced in the deep snow of winter.

However, some of the best onsens are not very far from Tokyo.

Onsens in Kusatsu, Gunma

Kusatsu is Japan’s premier onsen town, with steam rising throughout – you can even find free public baths. With dozens of resorts and ryokans, it’s close proximity to Tokyo make it the country’s most popular onsen destination. Plus, the Shinkansen to get there is covered by Japan Rail Pass.

Onsens in Hakone, Kanagawa

Until Kusatsu knocked it from its throne in 2022, Hakone had been the most-visited onsen town in Japan for the past 15 years. You’ll find numerous resorts, souvenir shops and restaurants – and one of the best views of Mount Fuji around.

Less than 2 hours from the nation’s capital, it’s the perfect Tokyo day trip or overnighter. The Odakyu Romancecar express train – with reserved seating only – gets you there in 80 minutes from Shinjuku for under 2,500 yen.

Onsens on the Izu Peninsula, Shizuoka

The Izu Peninsula in Shizuoka Prefecture is famous for its beaches and hot springs. The peninsula abounds with onsens, and some of them – like the beachside resort town of Atami – are just 50 minutes from Tokyo Station.

But if you’re looking for a konyoku (mixed onsen) to enjoy with your partner, keep heading south to the tip of the peninsula. In the town of Shimoda, you’ll find Japan’s largest cypress bath at Sennin Buro Kanaya Ryokan.

Sennin Buro (千人風呂) literally means “1,000-person bath”. And it’s been in operation since 1867 – the year that Japan’s Edo Period came to an end. Women can join the men’s side (wrapped in a towel), but not vice-versa, and men don’t wear a towel or swimsuit.

The trip to Shimoda is just a 2-hour train ride from Tokyo and is covered by the JR Pass.

Onsens in Beppu, Oita

Located on the southern island of Kyushu, Beppu’s 2,000+ springs pump out more water than any other hot spring region in Japan. You’ll find everything from regular onsens and steam baths to mud baths and sand baths.

It’s about a 6-hour Shinkansen trip from Tokyo to Beppu or a 90-minute flight out of Haneda or Narita. The JR Pass gets you there, but takes an extra hour due to limitations on the trains you can take.) It’s no day trip, but for those looking for an unforgettable onsen experience, Beppu is worth the journey.


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