Paris is home to some of the best swing clubs in the world, which they call clubs libertins. They are basically nightclubs with benefits (with rooms where you can have sex). These swing clubs are not at all an underground scene: they are very fancy places, with high-level services and facilities.
Cap d’Agde is the world capital of swing. There is no place like it: thousands of locals and tourists dedicated to sex in parties, nightclubs, beaches, and saunas. It is a unique experience.