Sashikino Onsen Enjin no Yu (Yuinchi Hotel Nanjo)

Verified by the editor

The best water in Okinawa on the evidence available. It is fossil seawater drawn from between 1,500 and 2,119 m down, blending two layers roughly 5 and 54 million years old, and the hotel states plainly that nothing is filtered, reheated or diluted - genuine free-flowing source water, which almost nothing else on the island can claim. About 80% the salinity of seawater, with a thick, oily feel from the metasilicic acid. The view bath on the Sashiki hillside looks straight out over the Pacific, blue by day and the lights of Nanjo by night. There is a canteen, a relaxation room and a spa, so you can stay a while. Getting here needs a car.

Every onsen on this site is scored against the same written rubric, and every score has been reviewed by the editor. The ones marked Visited were also bathed in personally.