I guess... should I write something about onsen?
Japanese culture makes a habit of visiting onsen, known in other countries as natural hot springs. The word is not often used to refer to the hot springs themselves, but rather to nearby inns that funnel the natural spring water into private bathhouses, where patrons can relax. In my time in Japan, I have only visited about half a dozen onsen, but there are thousands of them in Japan, ranging from elegant to bus-stop quality. Most recently, I visited an onsen located in a pitstop in Yamagata Prefecture. It was located inside a giftshop, and crowded with patrons coming home from a climb up Mount Gassan.
The above picture is likely from a ryokan, which is an expensive old-style inn where people crossing the highways during the Edo Period would stay. This type of inn is still popular, even today. Below is a picture of the more likely scenario: a modern-style onsen located in a modern building, with large picture windows but no direct access to the outside. The women and men are separated by a high wall, though there is often a clearing at the top of the wall to allow vapors to pass though. In Japan, the symbol ♨ is often used to mark an onsen on a map or road sign.
Obviously, since the invasion of Western culture into Japan, the previous practice of mixed-gender bathing is no longer in effect. What few onsen remain that allow mixed-bathing are known as konyoku, and offer mixed-gender bathing only as an extra option, not as the norm. To ensure that the water is kept clean, each onsen contains a shower area between the baths and the locker room. Patrons are expected to clean every nook and cranny before entering the baths, including both shampoo and bodywash. In addition, wearing a swimsuit or taking a towel into the water is against standard protocol. Most patrons bring a small towel that they put on their heads or leave on the side of the bath, out of the water.
Honestly, it's a great experience that I've had many times, in various locations and at varying levels of excellence, and I recommend anyone try it at least once. For us westerners, there is the hurdle of public nudity to overcome, even when it involves bathing nude with members of your own sex. Once you've realized that no one cares that you're naked, the hardest part is over and you can enjoy a nice, long, warm soak. Yokatta na...