From a lord's tea house to a town for cures
In 1706 a tea house was built for the Nakagawa lords of the Oka domain, and Nagayu became their bathing retreat; the name Gozen-yu, 'the lord's bath', recalls this. In 1933 Dr Matsuo Takeyuki of Kyushu Imperial University introduced the water to science as an iron-bearing carbonated spring. The town was designated a National Health Resort Hot Spring in 1978, and again in 2015 as part of the Taketa group.[4]
Germany as the model: drink it, soak long
Twinned with Bad Krozingen, a German spa that uses carbonated bathing therapeutically, Nagayu built its identity around drinking the water and soaking long. Gozen-yu, opened in 1998 in a German style, draws on three sources and lets you drink at the entrance fountain and at every spout inside. The town counts 22 day-bath facilities (tourism association).[5][3][2]
Why 32 degrees
Carbon dioxide leaves water as it warms. That is why the 42 °C indoor bath shows almost no bubbles while the 32 °C pool coats your skin with them. Lamune Onsen (2005, by Terunobu Fujimori) turns this into the building's idea: a tepid outdoor pool beside a hot indoor bath. The pool's free CO2 is reported at 1,380 mg, above the 1,000 mg/kg therapeutic threshold. Gani-yu, a lone tub in the river, is the kind of thing only a town awash in hot water would have.[1][3][4]
