Multiple realities
(covers information from several alternate timelines)
Bathing or ablution was the act of cleaning and maintaining one's personal hygiene, that often had relaxing effects. For humanoids, this was often done in a bath tub or shower, using water; or in a sonic shower. (TOS: "The Naked Time", Star Trek: The Motion Picture, VOY: "Caretaker") It was sometimes aided by a servant. (DIS: "The Wolf Inside")
Some cultures used mud baths or protein baths as a method of relaxing. (TNG: "Birthright, Part I", "Cost Of Living", DS9: "Who Mourns for Morn?")
Bathing could take place in a bathroom, or a specialized establishment such as the Hoobishan Baths on Trill. (DS9: )