Nasuonsen Shikanoyu Hot Spring

Shika-no-yu (鹿の湯) is one of Japan's oldest continuously operating hot springs, with roots going back about 1,300 years. The wooden bathhouse sits astride the Yukawa stream in Nasu Yumoto, and everything here is stripped back to the essentials: indoor gender-separated baths, no soap or shampoo, no outdoor tub, no frills. What it does have is six pools of different temperatures for men (five for women), all fed by a direct, unfiltered flow of milky sulfur water that turns the skin smooth and faintly sulfurous. The traditional way to bathe is short dips with cooling-off breaks in between, repeated over an hour or so. No shampoo is sold; a rinse before entering is all the prep you need.