I read the most recent (English translation available) "The Hangman's Daughter" novel not too long ago in which much of the action takes place in the bathhouse that is operated by the Hangman's sister and her husband.
How often do we find a bathhouse as a part of the setting in an AD&D adventure? Almost never. There are usually pubs, bars and taverns galore. There are stores of various type, Sheriffs offices and blacksmiths abound.
Rarely, if ever, do you see a bathhouse though, even in passing, let alone as a key location to investigate.
What appeal does a bathhouse bring to an adventure? Just about everyone from all classes would visit bathhouses way back when. Not only were the bathing tubs and pools used for relaxation, but often were a front for other, often nefarious, activities.
Smuggling, human trafficking, drug dealing, prostitution and more went on behind closed doors in bathhouses. You could find all the gossip you ever wanted to hear about just about anyone in a town or city at a bathhouse. Medical services were sometimes to be found in bathhouses.
Bathhouses weren't just a place with a few old fashioned bathtubs in them, though some were. Many, if not most, offered amenities such as saunas and hot tub-like setups.
Have you ever included a bathhouse in one of your homebrew adventures? I plan to write one into an upcoming game soon, not too baudy, the players are 12 and 14 so PG-13 is about the most "steamy" (get it, bathhouse-steamy? didja get it? huh? huh?) they are going to get out of me.
Even toning it down a bit, I can think of several interesting things that can happen in a bathhouse.
Tell me about your bathhouse adventures, past or planned.