Washing and thermal body treatments with steam and accessories such as a bunch of birch branches has been traditionally carried out in banyas. This traditions were born in rural areas, Russia being a spacious country with farming population dominating until World War II. Farmers did not have inside their log cabins running water supply and hot bathtubs for washing their bodies, so they either used for their washing heat and space inside their Russian ovens or built from logs, like the cottage itself, a one-family banya bath outhouse behind their dwelling on the family’s land plot. It was usually a smallish wooden cabin with a low entrance and no more than one small window to keep heat inside. Traditionally, the family washed their bodies completely once a week before the day of the Bible-prescribed rest (Sunday) as having a (steam) bath meant having to get and bring in a considerable amount of firewood and water and spending time off other farmwork heating the bathhouse.
With the growth of Russian big cities since the 18th century, public baths were opened in them and then back in villages. While the richer urban circles could afford having an individual bathroom with a bathtub in their apartments (since the late 19th century with running water), the lower classes necessarily used public steambaths – special big buildings which were equipped with developed side catering services enjoyed by the merchants with farming background.
Since the first half of the 20th century running unheated drinking water supply has been made available virtually to all inhabitants of multy-storey apartment buildings in cities, but if such dwellings were built during the 1930s and not updated later, they do not have hot running water (except for central heating) or space to accommodate a bathtub, plumbing facilities being limited in them only to a kitchen sink and a small toilet room with a toilet seat. Thus the dwellers of such apartments, on a par with those living in the part of pre-1917-built blocks of flats which had not undergone cardinal renovation, would have no choice but to use public bathhouses.
Since the 1950s in cities, towns and many rural areas more comfortable dwelling became a nationally required standard, and almost all apartments are designed with both cold and hot water supply, and a bathroom with a bathtub, but a percentage of people living in them still go to public steam baths for health treatments with steam, tree branches, aromatic oils and for social activities such as meeting friends and having a chat, a drink (usually, beer) and/or a snack in the dressing/cooling room, as was archetypally shown in a 1970s New Year evergreen comedy film The Irony of Fate, or Enjoy Your Bath!
https://en.wikipedia.org/wiki/Public_bathing