Hidden Wonders | A Cave Onsen Deep in the Mountains of Fukushima

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Tsuchiyu Onsen is a mountain hot spring town with many traditional inns, located about 16 kilometers (roughly 10 miles) west of Fukushima city. Just 1.5 kilometers further along a narrow mountain road is Kawakami Onsen, an inn with over 400 years of history.

The inn is deep in a region called Okutsuchiyu Onsen. This hidden gem is famous for its unique Hanten Gankutsu Bath — a hot spring bath carved directly into the rock. As the name suggests, half of the bath is open-air, and the other half is inside a cave. Soaking in this mysterious tub feels like stepping into another world. But why is there a hot spring inside a cave?

Classic Inn and Cave Onsen

“Kawakami Onsen” refers to both the hot spring and the inn itself. The inn’s wooden building has a charming, retro feel. The hot spring water is around 57–60°C (135–140°F). It is said to help with nerve pain, joint pain, and chronic digestive issues.

Toshihide Abe, the 16th-generation owner, laughs as he says, “People say it feels like coming to grandma’s house.” The inn was founded in 1615, but was moved to its current location at some point. Records are limited, and Abe admits, “We don’t know the exact date it opened here.”

The cave bath offers a unique escape from everyday life. (©Sankei by Nobuo Serizawa)

Bubble-Economy Inspiration

Open-air baths became very popular more than 35 years ago, during Japan’s economic bubble. Kawakami Onsen didn’t have an outdoor bath at that time. Abe’s late father, Yoshisuke, who was the previous owner, decided to build one to attract visitors. He came up with a bold idea — combining an open-air bath with a cave bath carved into the rocky cliff.

“At the time, cave baths were rare. Only about ten existed in Japan. I thought, ‘What on earth is my father thinking?'” Abe recalls. The bubble era also brought a construction boom. Craftsmen were in high demand and short supply. The work was slow, done with a mix of heavy machinery and hand labor. “It took about three years to finish,” Abe says.

For the bath itself, Yoshisuke insisted on using Hiba cypress wood from Aomori Prefecture. Most open-air baths are made of stone or rock. A wooden tub is rare and eye-catching but requires a lot of maintenance. Still, the bath’s unique atmosphere made it popular. Earlier in 2025, it ranked third in “Retro Hot Springs That Feel Straight Out of a Movie,” a list published by the travel site Jalan.

Japan 2 Earth Masthead Banner An Adventurous Experience

I tried the Hanten Gankutsu Bath myself. The tub is T-shaped, with the vertical section extending about six meters into the cave. The rough rock walls give it a rugged, natural feel, and the lighting adds to the mood. The water is 85 cm (about 33 inches) deep — deep enough to cover the waist of someone about 170 cm tall. The cave setting made me feel like an adventurer, but it was also strangely relaxing.

The inn also has a “Mannin Bath,” a pool-like bath about 10 meters (33 ft) long and 4 meters wide, with a maximum depth of 1.2 meters (3.9 ft). Both baths offer inflatable rings. Even adult guests sometimes play in them like children.

Abe says, “Hot springs are living things. Their temperature and flow change day by day.” He hopes visitors enjoy the inn’s hidden, cozy charm. The Hanten Gankutsu Bath and Mannin Bath switch daily between men and women, which means guests staying overnight can enjoy both. Day-trip bathing is also available.

Author: Nobuo Serizawa, The Sankei Shimbun

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