Nagayu Onsen

Nagayu Onsen in Taketa City, Oita, is one of Japan's most naturally carbonated hot spring areas, with dissolved carbon dioxide levels among the highest of any spring in the country. Tiny bubbles cling to your skin as you soak, said to improve circulation and lower blood pressure. The centerpiece is Ramune Onsen, a public bath named after fizzy soda because the water visibly sparkles as you enter. A handful of ryokan and bathhouses are scattered through the quiet village along the Eria River. Nearby Taketa City adds a well-preserved samurai district and the atmospheric ruins of Oka Castle if you want to pair the soak with some history.