[Rendello]

Interestingly, onsen were traditionally mixed sex until relatively recently (Meiji Restoration). As of now, mixed bathing is banned [1], though hidden in the Wikipedia notes is this:

> due to varying interpretations of terminology and local ordinances, rare instances of mixed bathing still exist at places like Tsurunoyu Onsen where the water is opaque.

1. https://en.wikipedia.org/wiki/Onsen#Mixed_bathing