Some of them are like a cross between a bar, a gym, and a hotel. Many have theaters, private rooms, group rooms, and some even have stages and galleries. Some are really nice, but most are pretty basic.
There have been some successful heterosexual bathhouses, but it's a much more difficult dynamic as women (gay or straight) tend to like such scenes less than men (who are generally pigs regardless of orientation).
San Francisco has two major heterosexual clubs, one of which is a private club of the Hells Angels, and another of which is notorious for all the crazy stuff you see on TV like bondage, pony girls, and other kink.