Hike to the source of Japan’s most powerful onsen

Indoor onsens are very nice, but for something truly wild why not take a Numajiri ‘Extreme Onsen Tour’ and hike to the source of Japan’s most powerful onsen?

This is the real deal, high in a valley on Mt Adatara. Mt Adatara is actually a 9km long range made up of numerous active volcanoes, rising to 1700m. From the western Nakanosawa side you look across to the sharp peak of Mt Bandai, created by a massive eruption in 1888 that also formed numerous lakes. Japan’s 4th largest lake, Lake Inawashiro, lies in the distance.

The hot stream on Mt Adatara  is rated Japan's most powerful onsen
Hot stream at Nakanosawa Onsen © Aizu Dream Development

This whole scenic Aizu region of Fukushima Prefecture offers plenty for visitors, especially active ones. Autumn is the perfect time to make the trip to enjoy magnificent colours through the forests. What better way to view them than hiking to a hot stream in a high valley?

The source of the onsen was discovered 380 years ago at 1250m above sea level. With a flow of 13,400 litres per minute, according to research done by the Aizu Insurance Office, it is the most powerful in Japan.

The water colour varies day to day from clear to milky, with a PH level between 1.7 – 2.1 that’s renowned for its therapeutic properties.

Taking a foot spa in the hot rvier on Mt Adatara, Nakanoswa Onsen
Soothing tired feet © Aizu Dream Development

The track heads out from Numajiri Ski Area, which claims to be Japan’s oldest ski area, on the lower slopes, winding up the valley past a hot water waterfall to the upper valley where a series of boardwalks have been built along and over the hot stream.

The hike to the springs can be done in an hour or so stopping to take in the sights along the way. From spring to autumn it’s easy enough for any normally mobile adult or child over 10 to negotiate. Tours don’t operate in winter due to heavy snowfall covering the track, but it is possible to access the springs with a guide and more effort.

You can dip your feet at the source, which is enough for many, or (Japanezy’s preferred option) go right in. Be careful, check with the guides and your own testing that where you choose is cool enough to get into. It’s definitely one of the hottest onsens we have ever tried, inside or outside.

The Nunajiri Extreme Onsen Tour has been developed by local travel specialists ADD (Aizu Dream Development) who specialise in promoting the Tohoku area to international markets. They have English, Thai and Taiwanese speaking staff and can customise tours in the region to suit.

Nakanosawa Onsen village nearby has a range of comfortable accommodation to suit different tastes and budgets. The villagers have been tapping into the hot springs for hundreds of years, and now have a long pipeline running down the side of the valley to deliver it straight to homes and ryokan there.

Among many excellent options to stay at, our favourite is the Numajiri Lodge.

The upper section of the hike is along boardwalks built by the villagers © Aizu Dream Development

For more on Nakanosawa, where to stay, dine etc check our feature