Onsen expert and researcher who’s visited thousands of hot springs gives us a gift of knowledge for Good Bath Day.

Between Japan’s abundance of geothermally heated water and love of a nice relaxing soak, you’re spoiled for choice when it comes to onsen/hot springs. And while we’re always up for a hot spring run, there are simply too many options to choose from to make “all of them” a viable selection for our next trip.

So to help narrow down the list, and also to celebrate the quasi-holiday of “Good Bath Day” (observed on November 26, since the numbers 1, 1, 2, and 6 can be pronounced in Japanese as “ii furo,” which also means “good bath”), we turned to an expert.

Yasuaki Goto (pictured above) is a medical doctor and also chief researcher for the Japan Health & Research Institute, a general incorporated foundation that studies, among other things, the medical benefits of hot spring bathing. Goto is also, personally, a huge hot spring fan, having visited more than 2,000 hot springs around the world over the last 30 years, earning him the nickname Furofessor in Japanese, meaning “Professor Bath.”

We asked Goto to tell us the eight most memorable hot springs he’s been to in Japan, and he was happy to share with us the following list, along with his reasons for each pick.

● Zao Zenshichi no Yu (Zao Onsen, Yamagata Prefecture)
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I recommend this place for onsen fans who’re seeking stimulation. The Zao Onsen area’s sulfurous hot springs produce highly acidic waters. As you approach the town, you can notice the smell of hydrogen sulfide, which resembles rotten eggs, and the three public baths, called the Kawarayu, Kamiyu, and Shimoyu, have water between 42 and 45 degrees Celsius (108 to 113 degrees Fahrenheit). The water gives a stimulating tingling sensation, and it often lingers even after you get out of the bath.

Zenshichi no Yu’s owner, Zenshichi Okazaki, is the 13th generation to run the onsen and its attached ryokan [inn], and the bath water is 100-percent straight from the spring, with no other cold or hot water added. They also have multiple private baths kept at different temperatures, so that you can choose the one that’s just right for you.

In addition, if you’re walking around the town of Zao Onsen, Goto says to stop by Takayu, a parlor where you can play “hot spring table tennis.” In addition to regular rackets, you can play with wash buckets, slippers and other items, and also dine on soba noodles or grilled mutton.

● Senkyoro (Owakudani Onsen, Hakone, Kanagawa Prefecture)
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When looking at the total therapeutic effects of hot springs, we consider nor only the water and the minerals in the liquid, but also the water vapor and other gases present. In Hakone’s Owakudani area, volcanic gases combine with the subterranean water, which then flows to the Sengokuhara and Gora parts of town. That same gas is what creates the famous black eggs boiled in the hot springs of Owakudani, the ones that people say will increase your lifespan by seven years if you eat one.

Senkyoro, is in the Gora area, has 100-percent pure hot spring baths, which are rich in acidic calcium sulfate and chloride, which makes the water white and cloudy with a stimulating effect, while still being smooth to the touch.

● Senninburo Kanaya Ryokan (Rendaiji Onsen, Izu, Shizuoka Prefecture)
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Kanaya Ryokan is a great place for when you really want to take your time and relax at an onsen. The Senninburo (“Thousand-Person Bath”) is 15 meters (49 feet) long by 5 meters wide, and one meter deep at its deepest part, making it one of the most spacious hot spring baths in all of Japan. Even then, all of the water is 100-percent pure from the spring source!

It’s a simple alkaline hot spring, so the water is gentle to the skin. And the bath is just so big that’s it’s only natural to want to try swimming in it. Of course, you shouldn’t do that if there are a lot of people around, but doing a little wading is one of the unique fun points of this bath. The men’s and women’s changing areas are separate, but mixed bathing is possible here too. There’s also an observatory on the inn’s premises, which is a great place to see views of the moon or the starry night sky.

● Izu no Odoriko no Yado Fukudaya (Yugano Onsen, Izu, Shizuoka Prefecture)
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There are many connections between onsen and literature, and if you like books I recommend this place, since the hot spring town is the setting for The Dancing Girl of Izu, and it’s said that the author, Nobel Prize winner Yasunari Kawabata, stayed at this inn, which inspired a scene in the story. The room on the second floor of the inn, now called Odoriko No. 1, is the room from which the story’s dancing girl is seen jumping into the outdoor bath.

The inn is also famous for the Kaya bath, located in the basement of the main building, which has refreshing sulfate water.

● Baikunro (Umegashima Onsen, Shizuoka Prefecture)
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This is a pace for those who want to feel like they’re melting right into the bath. The town of Umegashima is high up in the mountains, traveling upstream beside the Abegawa River on a road so narrow that there’s barely room for two cars to pass by each other, but it’s a hidden paradise for onsen fanatics.

The spring source is under Yuno Shrine, and the water, rich in alkaline and sulfer with a pH of 9.6, has a noticeable milky texture, and it flows directly into the cypress bathtub of the Kin no Yu bath at the Baikunro bathhouse.

Soaking in the water, it feels like you’ve had a delicate veil draped over you, and it’s so comforting that you’ll feel like you could stay in there forever. When you do get out, though, the soba noodle restaurant at Yuno Shrine is a good choice, and there are also places to eat locally caught game like deer and wild boar.

● Ramune Onsen, Daimaru Ryokan Annex (Shichirida Onsen Shitanyu, Nagayu Onsen, Oita Prefecture)
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There aren’t many carbonic hot springs in Japan, but this is my pick for one of the best. Ramune Onsen’s open-air bath, as one of the baths in this town that contains a large amount of carbonic acid in its water, feels like it’s wrapping your body in champagne-like bubbles as soon as you step in.

I always look forward to that sensation, and also the fun of wiping all the bubbles away in a big sweep of my hand. Watching the bubbles float up in the bath and listening to them fizz is fun even for adults.

Actually, the water at this hot spring doesn’t have such a high temperature, but the bubbles promote good blood circulation, which warms up the body. A lot of commercially available fizzy home-use bath salts take inspiration from Nagayu Onsen’s baths.

● Jigoku Onsen Seifuso (Jigoku Onsen, Minamiaso, Kumamoto Prefecture)
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In 2016, the town of Minamiaso was hit by an earthquake, heavy rain, and landslides. The Jigoku Onsen hot spring district suffered immense damage, but this bathhouse with a spring right below it, narrowly avoided destruction. It reopened for day-use bathing in 2019, and the attached inn began welcoming overnight guests again in 2020. Run by three brothers, the bath is now a mixed-gender facility.

● Kannawa Mushiyu (Kannawa Onsen, Oita Prefecture)
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There are around 3,000 different hot springs in Oita, which is about 10 percent of the total for all of Japan. Even in that environment, Kannawa Onsen stands out as a town with a great atmosphere, with steam rising up into the air. The Kannawa Mushiyu (steam bath) is someplace I especially recommend. You could say it’s a kind of Japanese-style sauna, where you lie down in a stone chamber filled with steam. After an eight-minute session, you’re sure to feel thoroughly refreshed. In Kannawa Onsen, they even use the steam from the onsen for cooking food, a style called “jigoku mushi,” and some locals say that eating it cleanses your body from the inside out.

Thanks, Professor Bath! With winter just around the corner, we plan on spending as much time as possible soaking in Japan’s hot springs, especially now that we’ve got eight destinations on our to-bathe list.

Photos ©SoraNews24
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