Sento - Public bath houses

Japan has public bath houses which people go to take a bath. The rise of the sento, or bath house, really starts in the town of Edo (currently called Tokyo) during the Edo period. Private heated baths were outlawed because of the fear of fires, so if people wanted a hot bath they either needed to go to a hot spring or a bath house. Until the 1950's, these bath houses were mixed sex. A law was placed requiring bath houses to be sexually segregated, mostly because of pressure from westerners. Since then they are divided by a wall, or if a really old one, a curtain.

Sento's served as more than a place to get clean. They were a gathering place for conversations, gossip, and general interactions. Cleanliness was also a very important part of their religion so it was also seen as a religious activity.

When you go to a public bath bring your own soap, shampoo, hand towel, and wash bowl. Must wash thoroughly before getting into the tub of hot water, soap is not permitted in the tub. This is especially important so I'll mention it twice wash thoroughly before entering tub.

With the increased western influence, rising prices, and more households having private bathes, these public bath houses have been in decline. To counteract this decline, operators of bath houses have been adding additional amenities, such as coin-operated laundry machines, saunas, coffee shops, game rooms, reading rooms, etc.

Random trivia:
Temperature of the water is usually between 105 and 108 degrees Fahrenheit.
They can often be recognized by large smoke stacks since a lot of them are wood heated.
I could write more but the wikipedia page for it is quite good, so have a look at it: Wikipedia page for Sento

Sento are seen in many manga and anime because they allow for fanservice. Ranma has several storylines set in public bath houses.