There were four kinds of `sweating treatment' (sambhàraseda); using steam made from water with certain herbs it, steam made from water with cannabis in it, `great sweating' and udakakottaka, which may have meant soaking in a tub of hot water (Vin.I,205).
Like many people before and since, the Buddha recognized the medicinal value of cannabis and he recommended it as a cure for rheumatism. The patient should be placed, he said, in a small room filled with steam from a tub of boiling water and cannabis leaves (bhangodaka), and inhale the steam and rub it on the limbs (Vin.I,205).
Indian Buddhist monks introduced the sauna to China from where it spread to Korea and eventually to Japan. The Daito Seiiki Diary by Genjo Sanzo (602-664 CE), mentions Chinese Buddhist temples with saunas that were open to the public. These saunas also provided medicine and food for the benefit of the poor and the sick. From the introduction of Buddhism in Japan during the Nara Period, many of the larger temples had saunas from which the modern baths, the sento, evolved. In the beginning these baths were meant mainly for the monks but occasionally they were open to others. Records mention that the wife of the Emperor Shomu, Koumyou Kougou (701-760 CE) allowed the sick the opportunity to bathe six days every month and even personally washed them. From the Kamakura period (1185- 1333), it was normal to make temple baths available for the sick. When public saunas and baths were established away from temples they continued to be built in the style of temples, a tradition that continues even today. Since the 1960s when Japanese houses were more commonly designed with bathrooms, public saunas and baths have declined in popularity."
Already during Buddha's lifetime monasteries or viharas, owned by the Sangha, had saunas or bath houses built on their grounds.
source: https://www.buddhisma2z.com/content.php?id=482 (Saunas)
https://www.buddhisma2z.com/content.php?id=68 (Cannabis)
