noun
stone sauna; bedrock bathing
A spa treatment where one lies on a heated natural stone slab, often covered with towels, to promote sweating and relaxation.
週末に岩盤浴に行ってリラックスした。
I went to a stone sauna on the weekend and relaxed.
Compound of 岩盤 (ganban, 'bedrock') and 浴 (yoku, 'bathing').