What' Ganban-Yoku (岩盤浴, Bedrock bathing）?
The bath, not using hot water - It's ganban-yoku (bedrock bathing)!
Ganban-yoku is a method of keeping fit that involves lying down on a heated slab of rock that is embedded in the ganban-yoku room floor. Ganban-yoku is also referred to as "bedrock bathing without hot water". You can get more perspiration than a sauna from ganban-yoku.
The ganban-yoku slabs made by KIHOUSEKI etc. are warmed by the heater installed under the slabs, and emit far-infrared rays and negative ions.
Far-infrared rays penetrate the human body and are absorbed by cells causing a number of reactions such as dilation of blood vessels which improve blood circulation, speed up the metabolism and help eliminate wastes.