Hot Springs in every house
Japanese style bath tubs (ofuro) are requirement in Japanese culture, but you have to take a shower and get clean before you can get in the tub. It's not about becoming clean, it's about soaking in very hot water and relaxing. In most households the tub is fulled and stays warn, then in order by household rank everyone takes a turn starting with guests, elders, father, kids then wife. Yes, if you stay late in at someone's house you might be invited to soak and relax and you might even get a few kids thrown in.
Ofuro is actually a personal hot spring (Onsen) that one can visit everyday, but most people in Japan visit onsen often, it's no shock when looking at advertisement pictures in almost all magazines, at the train stations and on the walls of the trains. Japan loves it's onsens, in the northern areas the monkeys will soak for hours in the natural hot springs in pools adjacent to humans. Onsen trips are popular destinations for company trips, school classes (you have never seen bedlam till the peaceful onsen your visiting gets overrun by hundreds of middle school girls), families and reunions of old friends.
A few thing to know about going to an onsen;
Men and woman are split to different areas when bathing, there are a few that have mixed pools or even privet outdoor pools attached to a traditional tatami style room.
Every one is naked, get over it, it's about relaxing and talking to people and enjoy the escape from the fast pace of modern life (hadaka no tsukiai).
My first experience was years ago on a family trip to Awagi Island, we stopped off at a small onsen. Shinta at 5 years old at the time was left to teach me the proper educate of this most honored ritual. At that point I had been reading about Japanese culture and understood the basics, you get there, put your stuff in a basket, wash yourself very well, then go over take a bowl of water from the hot spring and rinse, then slowly get in the 42'c water and quietly enjoy the peace and quite, then go to the next area and repeat, all very Zen. So, he got us locker put all of our stuff in it and grabbed key, quickly headed to the wash area, sat me on a small stool showed me the soap and how to use the water controls, then in an burst of energy he did the fastest wash job on the planet ( still not sure if the bar of soap touched his body) ran over grabbed a bowl of water and poured it over his head as he dove into the hot hot hot spring. I finished washing off and joined him in the spring where he was sitting, then just as I got settled Shinta jumped up and started to collect all the small stools and bowls and pile them up under water towards the middle of the pool. The just as I was almost relaxed, he ran over showed me the key to the locker and stated he was done. Thus ended my first trip to an onsen and a rather stressful Zen experience.