noun
lava bath; bedrock bath; heated stone sauna
A type of sauna or spa treatment where one lies on a heated slab of rock, sometimes called a bedrock bath or lava bath.
このスパでは溶岩浴が人気です。
The lava bath is popular at this spa.
溶岩浴で体が温まりました。
My body warmed up in the bedrock bath.
Compound of 溶岩 (yōgan, 'lava') and 浴 (yoku, 'bath').