Kin no Yu

Kin no Yu is a public bath in Arima Onsen, one of Japan's oldest spa towns with a history of over a thousand years. It draws Arima's kinsen ('gold spring'), an iron-and-salt-rich spring water that is colorless when it first emerges but oxidizes on contact with air into a distinctive reddish-brown; the source can reach up to 98°C, and its salt concentration runs roughly 1.5 to 2 times that of seawater. The bathhouse is named for this golden-brown water, distinct from Arima's clear, carbonated ginsen ('silver spring').