Seki Onsen Asahiya Ryokan

Asahiya Ryokan sits at the foot of Mt. Myoko in Seki Onsen, at an elevation of roughly 900 meters. The spring is said to have been opened by the monk Kobo Daishi and was later prized during the Sengoku period as a hidden hot spring (kakushi-yu) of the Echigo warlord Uesugi Kenshin. The inn, formally known as 'Iyashi no Yuyado Asahiya', is a long-established ryokan that has preserved its distinctive reddish-brown cloudy waters.

The water is a sodium chloride-bicarbonate spring (formerly classed as an iron-bearing saline spring), with a source temperature of 48.6°C and a near-neutral pH of 6.3. It gushes at an abundant 510 liters per minute and is a completely undiluted, unheated, non-circulated, and non-chlorinated 100% free-flowing (kakenagashi) spring. Its high iron content oxidizes on contact with air, turning the bath a reddish-brown that warms the body to the core and keeps it warm long after bathing. Note that its source is separate and independent from that of neighboring Tsubame Onsen.

Besides an indoor bath available year-round, an open-air bath can be enjoyed seasonally from mid-May to late October. Day-trip bathing runs from 9:00 to 17:00 at 500 yen for adults and 300 yen for children. Overnight stays start in the low 10,000-yen range with two meals, and the cuisine featuring seasonal Myoko produce paired with local sake is well regarded.