Rokugo Dote Hot Springs Bathhouse
The natural hot spa waters of this area are brown in colour. Leaves your skin smooth. The temp. is 44 degrees C! There are also 39 degree C bath water to soak, though the lower temp hot water is from the tap, not natural mineral. Main mineral component is Sodium Bicarbonate. See website for details (sorry, only in Japanese):
Rokugo Dote Station on the Keihin Kyuko Line. From Kawasaki Station, one stop toward Tokyo on the local train.