An Onsen (温泉) is a term for hot springs in the Japanese language, though the term is often used to describe the bathing facilities and inns around the hot springs. As a volcanically active country, Japan has thousands of onsen scattered along its length and breadth. Onsen were traditionally used as public bathing places and today play a central role in directing Japanese domestic tourism.
Onsen are a central feature of Japanese tourism often found out in the countryside but there are a number of popular establishments still found within major cities. They are a major tourist attraction drawing Japanese couples, families or company groups who want to get away from the hectic life of the city to relax. Traditionally, men and women bathed together but single-sex bathing has become legalized as the norm since the opening of Japan to the West during the Meiji period. Mixed-sex bathing persists at some special onsen (konyoku) in the rural areas of Japan, which usually also provide the option of separate "women-only" baths or different hours for the two sexes. Children of either sex may be seen in both the men's and the women's baths.
- At an onsen, all guests are expected to wash their bodies and rinse themselves thoroughly before entering the hot water. Bathing stations are equipped with stools, faucets, wooden buckets, and toiletries such as soap and shampoo; nearly all onsen also provide removable shower heads for bathing convenience. Entering the onsen while still dirty or with traces of soap on the body is socially unacceptable.
- Bathers are not normally allowed to wear Swimsuits in the baths. However, some modern onsen with more of a waterpark atmosphere require their guests to wear a swimming suit in their mixed baths.
- Onsen guests generally bring a small towel with them to use as a wash cloth. The towel can also provide modesty when walking between the washing area and the baths. Some onsen allow one to wear the towel into the baths, while others have posted signs prohibiting this, saying that it makes it harder to clean the bath. It is sometimes against the rules to immerse or dip towels in the onsen bath water, since this can be considered unclean. In this latter case, people normally set their towels off to the side of the water when enjoying the baths, or place their folded towels on top of their heads.
- Onsen vary from quiet to noisy, some play piped music and often feature gushing fountains. Bathers will engage in conversation in this relaxed situation. There are usually prohibitions against rowdiness in the washing and bathing areas of onsen. A small amount of excess energy and splashing around is usually tolerated from children, however.
- "Wani Otoko" ("Crocodile Man" or "Alligator Man") is the term used to refer to a man conducting lecherous activities in an onsen (purposeful voyeurism, groping, unsolicited sexual activities, etc)