Nagayu Onsen Daimaru Ryokan

Daimaru Ryokan is the oldest inn of Nagayu Onsen, standing beside the clear Seri River in Naoiri, Taketa City, Oita Prefecture. Founded in 1917, it has welcomed many writers and poets, including Tekkan and Akiko Yosano, Ujo Noguchi, Katai Tayama and Jiro Osaragi. Nagayu Onsen appears in the eighth-century Bungo-no-kuni Fudoki and is renowned as one of the world's finest iron-bearing carbonated springs; the inn also operates the celebrated external bathhouse Lamune Onsenkan.

The water is a magnesium-sodium-calcium bicarbonate spring with 3.745 grams of dissolved minerals per kilogram and a yield of about 450 liters per minute. The inn's own source, Tei-no-Yu, discovered by the third-generation proprietress, emerges at 46.7C and is poured undiluted into the bath as free-flowing kakenagashi, giving a cloudy brown water with a faint carbonated taste. Cups are provided so guests can also drink the spring water.

Bathing facilities include the all-hinoki open-air main bath Tei-no-Yu and three private family baths overlooking the river. Day-trip bathing costs 500 yen for adults and 300 yen for children aged three through elementary school, open 11:00-17:00; a private bath is 1,500 yen per hour. Overnight stays with two meals start in the 14,000-yen range, with free parking for 30 cars. Open year-round.