Nakamuraya Hotel

A small inn at Seki Onsen in Niigata with a striking open-air bath: the iron-rich sodium chloride water runs a vivid reddish-brown, which deepens when you stir up the settled minerals at the bottom. The spring has been flowing since the Edo period and the 女将 (okami, proprietress) is known for managing access thoughtfully, often arranging solo or near-private soaks for day visitors. The outdoor bath sits in a forested setting and can close in deep winter due to snow.