There is a difference between "Bath Houses" and "Sex Clubs". A bath house, as I understand it, is simply a facility where adults of both sexes can go and enjoy the facilities in the nude, but it does not allow overt sexual activity.
My wife and I have been to a few of the former, the "legitimate" bath houses. There are usually more men than women (Surprise!) and the men do let themselves look at the nakedness of the women, but they are usually very discrete.
My wife and I were in the sauna, across from two men. At one point when she moved, her legs were apart and I could see the two men staring intently right into her crotch. When they looked up and saw that I was watching them look at her, they smiled nervously, as if worried about what my reaction would be.
I gave them a smile or reassurance, which said, I thought "Go ahead and look! She's naked, isn't she?" There have been numerous such incidents at these clubs, and also at nudist gatherings. I have observed that most husbands do enjoy knowing that the other men are looking at their wives' naked bodies, but that is as far as it goes.