stone bathtub
A bathtub made of stone, often found in traditional Japanese settings or hot spring resorts.
The inn's open-air bath had a large stone bathtub.
steam bath in a stone chamber
A steam bath taken inside a natural or man-made cavern or stone chamber, historically used for therapeutic purposes.
It is said that people in this area used to cure illnesses by taking steam baths in stone chambers.
Compound of 石 (ishi, 'stone') and 風呂 (furo, 'bath'). The exact historical origin of the steam bath sense is uncertain, but it likely refers to the use of stone chambers for bathing.