Hakusui Kosen Kurodakeso

Kurodakeso is a single secluded inn set in a valley on the northern foot of Mt. Kurodake, at the eastern end of the Kuju mountain range in Oita, where natural carbonated spring water bubbles up from the ground. In 1916 (Taisho 5), Teihei Ito and others obtained a license to sell the mineral water, and in 1933 (Showa 8) a lodging facility for treating skin ailments was established here. After the war it has continued to operate as Kurodakeso. The name Hakusui, meaning white water, is said to come from the way the water looks white when saturated with carbon dioxide, and the spring is known alongside nearby Nagayu Onsen as a noted source of carbonated water.

The water is a carbon-dioxide-bearing calcium and magnesium bicarbonate spring, with a source temperature of about 9 degrees Celsius, making it a cold mineral spring. Rich in natural carbon dioxide gas, it fizzes lightly on the tongue and carries a faint iron-like flavor. The bathhouse offers two kinds of tubs: a cold tub filled with 100 percent free-flowing source water, and a heated tub, so visitors can alternate between cold and warm bathing.

At this one-inn spot, day-trip bathing is available for 300 yen for adults, and overnight stays start from 5,000 yen with breakfast, or 7,350 yen with two meals. In summer the inn serves its signature dish of somen noodles chilled in freshly drawn natural carbonated water for 700 yen. Guests can also take home the mineral water from the grounds, and roughly 50 free parking spaces are available. As day-trip bathing has at times been limited to overnight guests in recent years, checking in advance is recommended.