Nagayu Onsen, Ōita: A Sparkling Bathing Experience in Kyūshū’s Fizziest Waters

The Most Carbonated Hot Springs in Japan

In the high country at the eastern foot of looming Mount Kujū in Kyūshū’s southwest Ōita Prefecture there is a remarkable hot spring resort town with an unusual claim to fame. It is the only hot-spring resort in Japan where you can soak in—and even drink, if you feel so inclined—naturally occurring, highly carbonated water. This is Nagayu Onsen, with dozens of “aerated springs” rich in sodium and magnesium scattered along the course of the Serikawa River. Nagayu was also the first hot-spring resort district in Kyūshū to declare that it would stop adding chlorine to its onsen waters and use only free-flowing spring water, meaning that you can indulge in this remarkable, pure carbonated water at any of the area’s baths.

Riverside hot-spring resorts in Nagayu illuminate the Serikawa.

Nagayu Onsen’s special claim to fame is the extremely high concentration of carbonic acid in its waters. At higher temperatures, carbonic acid breaks down more quickly into water and carbon dioxide, thus causing the water to lose its fizz in a short time. For this reason, carbonic acid hot springs are generally on the cooler end of the spectrum, topping out at around 30ºC. The concentration of carbonic acid in water from the springs of Nagayu, however, is uncommonly high, meaning the springs can be unusually hot—with temperatures from 30ºC to as high as 50ºC—and still provide nearly the maximum possible amount of carbon dioxide. Bathers in Nagayu’s unique waters absorb the gas through their skin, expanding the capillaries and improving circulation. This heats the body through and through and keeps them from getting the chills when they leave the bath.

Nagayu’s carbonated spring water.

The hot spring resort that boasts the most carbonated waters in all of Nagayu is Lamune Hot Spring, sometimes called the “soda pop” hot spring. This facility is named after the nostalgic soda pop drink ramune, first produced in Japan in the early Meiji era (1868–1912) and named after lemonade. The resort offers both a 32ºC rotenburo outdoor bath and a 42ºC indoor mineral bath. We recommend you use them both in rotation. The beautiful resort buildings, combining modern and traditional Japanese architectural elements, were designed by the famous Japanese architect Fujimori Terunobu (1946–) and are worth a trip in themselves.

The “soda pop” Lamune Hot Spring resort.

Lamune’s rotenburo open-air bath.

The real centerpiece of Nagayu, however, is the Gozen’yu hot spring facility, which describes itself as center for hot-spring therapeutic culture and draws from a water source once used by the local feudal lords. This day-use facility is conveniently located in the Nagayu Onsen highway rest area. Boasting eye-stopping Western design evoking the architecture of Germany, Gozen’yu has a long history of studying the health benefits of hot-spring therapy. This resort offers something for every visitor, from its large main bath to a rotenburo, a cold-water spring bath, a sauna, and even a family-sized private bath that you can rent just for you and your loved ones.

The Gozen’yu center for therapeutic hot-spring bathing.

Another of Nagayu’s best loved spots is the Gani-yu, or “crab bath,” a mixed-bathing outdoor bath sitting on the rocky banks of the Serikawa. Built of stacked rocks and stones, the tub was built in the shape of a crab, thus earning it its name. The bathing is free, and it is fine for the modest to wear swimsuits. As if this hot spring bounty were not enough, there are another three public baths available in the resort.

Nagayu’s riverside “crab bath.”

Access to Nagayu Onsen (from Beppu)

By car: Head south from the city center and get to Prefectural Route 51. Turn right on National Route 210, left on Prefectural Route 618 (the Bungo Highway), left on Prefectural Route 690 (the Okusan Skyline), and right on Prefectural Route 412 for Taketa. From there, follow the roads marked for Nagayu Spa to your destination. The drive is around 40 km (about 1 hour).

By rail: From JR Kyūshū’s Beppu Station, take the Nippō Main Line to Ōita Station (13 mins) and change to the Hōhi Main Line for Kumamoto. Get off at Bungo-Taketa Station (about 1 hour 10 mins) and take a taxi to cover the 14 km (20 min) to Nagayu.

Nagayu Onsen (Japanese language only): https://nagayu-onsen.jp/

(Originally written in Japanese. Banner photo: Taking the waters at the Gozen’yu hot spring center. All photos © Taketa City Tourism Association.)