Hole bath - Anaburo

...In this method, a hearth like a cave that people could enter was built from rough walls, green pine needles and green wood were burned inside, the ashes were raked out, and then rough straw mats moistened with salt bags or salt water were laid out on the surface, on which people lay down to enjoy the steam, and it was believed to have medicinal properties. Similar types of steam baths, in which earthen walls or stones are heated and water is poured over them to create steam, can be found all over the country under names such as rock baths, cave baths, cauldron baths, and salt baths, and since it is easy to take a steam bath in natural caves, it is thought that they have been practiced by common people for a long time. During the Nara period, bathing facilities were built in large temples under names such as greenhouses, greenhouses, and bathhouses....

*Some of the terminology that refers to "hole bath" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…これは，荒壁で人の入れる穴蔵のような竈を作り，中で青松葉，青木を焚き，灰をかき出してから塩俵や塩水をかけて湿らせた荒筵（あらむしろ）を敷き，その上に横たわって蒸気に浴するもので，医効があるとされていた。土壁や石を熱して水をかけて蒸気をたてるという類似の形式の蒸し風呂は，岩風呂，穴風呂，釜風呂，塩風呂などの名称で各地にみられ，天然の洞窟などでも簡単に蒸気浴は可能であるので，庶民の間では古くから行われていたと考えられる。奈良時代には大寺院に温室院，温室，湯屋などの名で沐浴施設が作られている。…

※「穴風呂」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報