In ancient Rome, thermae (from Greek θερμός thermos, “hot”) and balneae (from Greek βαλανεῖον balaneion) were facilities for bathing. Thermae usually refers to the large imperial bath complexes, while balneae were smaller-scale facilities, public or private, that existed in great numbers throughout Rome.
Most Roman cities had at least one – if not many – such buildings, which were centres not only for bathing, but socializing and reading as well. Bathhouses were also provided for wealthy private villas, town houses, and forts. They were supplied with water from an adjacent river or stream, or within cities by aqueduct. The water would be heated by fire then channelled into the caldarium (hot bathing room). The design of baths is discussed by Vitruvius in De architectura (V.10).
There are many, but some of the most accessible are in the UK, even in London. Specifically, the Billingsgate Roman House and Baths are now open again after slogging their way through the Covid Pandemic. And, of course, Bath itself is England’s most famous location for these stunning places.