A Radium Hot Spring Hidden in the Mountains of Kyoto

I lived in Europe for many years. 

Whenever I moved, there was one condition I always insisted on:

An apartment with a bathtub.

In many European homes, showers are standard and bathtubs are not. So when I finally found a place with a tub, I proudly told my Japanese friends in London.

That’s how much bathing matters to many Japanese people.

This deep love of bathing is closely tied to Japan’s geography. The country sits on an active volcanic belt, with abundant groundwater, geothermal heat from magma, and complex geology. As a result, all 47 prefectures in Japan have natural hot springs — even Okinawa in the far south.

If you ever visit Japan, I highly recommend experiencing an onsen. It’s not just a bath — it’s part of everyday Japanese culture.

Fudo Onsen — the red flags at the neighboring temple add to its eerie atmosphere.

One of Kyoto’s Highest-Radon Hot Springs

Among Japan’s many hot springs, the one I visited this time lies deep in the mountains of Kyoto’s Sakyo Ward: Fudo Onsen.

This is a rare type of hot spring known as a radium onsen, with a radon concentration of 28.83 Mache units, one of the highest levels in Japan.

Bathing while inhaling trace amounts of radon gas released from radium is believed to stimulate cells through low-dose radiation — a phenomenon known as hormesis. It is associated with improved immunity and enhanced natural healing.

“Kansai’s highest-ranking radium mineral spring — certified for bathing and drinking.”

A Place I Knew — but Never Dared to Enter

I had known about this hot spring for years. I had even passed by it before.

But:

Mountain setting 

Aging buildings 

An almost eerie quiet

It felt strangely intimidating.

I assumed I would probably never go.

Then one day, a doctor I met casually mentioned:

“After a night shift, I go to Fudo Onsen. It resets my body and balances my nervous system.”

It’s funny how a place suddenly feels accessible once you know someone who goes there.

Looks more like a large family home than a hot spring.

A Small Adventure by Local Bus

The onsen is deep in the mountains and usually reached by car. But my car wasn’t working well, so I decided to go by bus.

There is only one bus every one to two hours. Yet — as often in Japan — it arrived exactly on time.

As the bus wound along narrow mountain roads, I kept thinking, “I’m really glad I’m not driving.”

A 1954 Bathhouse Clinging to the Mountainside

When I arrived, the sense of stepping out of time was immediate.

An old wooden structure clinging to the mountain slope. It was built in 1954.

Inside were large tatami rooms on both sides, where elderly visitors lay resting under blankets. The atmosphere felt less like a facility and more like entering someone’s home from decades ago.

For a moment, I wasn’t even sure where to go.

Corridor of Fudo Onsen — I couldn’t photograph the tatami rooms because people were resting there.

The Unique Ritual of Radon Bathing

When I told the staff it was my first visit, they kindly explained the system.

Each guest is assigned a private low table space in the hall. 

You leave your belongings there and repeat:

bath → rest → bath → rest

It felt almost like a therapeutic retreat rather than a typical bathhouse. I suddenly felt like a “professional hot-spring user.”

Radon bathing is usually recommended in short sessions of 10–15 minutes to avoid overexposure.

I, however, unknowingly stayed in for a full hour.

Yet it felt incredibly comfortable, and I experienced no dizziness or fatigue. After bathing, I sat in the hall looking out at the mountain scenery, feeling as if I had slipped into another era.

It was a bit cloudy that day.

The Change That Came Five Days Later

At the time, I had been suffering from severe shoulder pain for three months. It was bad enough to stop me from working.

Right after the visit, I only felt slightly better.

But then — five days later — something unexpected happened.

I suddenly realised:

“My shoulder hasn’t hurt at all today.”

When I counted back, it was exactly five days after my visit to the radium onsen.

I had read that the effects of radon baths sometimes appear several days later. My experience matched that perfectly.

Radium spring water can be collected here beside Fudo Onsen.The stone basin is inscribed with the words “helping water,” a name rooted in local healing traditions.

An Otherworldly Side of Kyoto

Kyoto is famous for temples and gardens, but this hot spring revealed a completely different Japan.

Not a tourist site Deep mountain setting Showa-era architecture Therapeutic bathing culture Quiet, local atmosphere

I was amazed that such a place exists within bus distance of the city.

I have completely fallen in love with it.

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Written by Nori (NOTA)