Even though the country is arguably more technologically advanced than anywhere else on earth, this ancient ritual survives - and thrives.
I'm not talking about any old bath. No, what attracts me is the onsen (traditional Japanese bathhouse).
Like almost everything else in Japan, bathhouse use is governed by strict rules. Well, they're not really rules - more custom and etiquette. But thinking of them as rules reduces the likelihood of being remembered as an ignorant foreigner.
Bathhouses are part of the landscape all over Japan - in big cities and small rural towns, in business-oriented destinations as much as in holiday haunts.
Some are large and lavish establishments in major hotels. Others are tiny family-run businesses. Most obtain mineral-rich water from natural springs, which are numerous on these volcanic islands.
A few, in remote country areas, don't segregate the sexes. If you find yourself in such a place you just have to deal with it - and accept that you're totally naked among a bunch of strangers, some of whom will inevitably be of the opposite gender.
However, they couldn't care less that you're not wearing clothes. Japanese don't regard bathhouse nudity as an issue - and consider it puzzling, even amusing, that some foreigners make a fuss about it.
These days, it's usual to segregate the sexes - though not to do away with nudity. In cities as well as in country areas commonly frequented by tourists, the onsen you visit will almost certainly have separate facilities for men and women.
For example, on my most recent bathhouse visit - to an onsen at the Hilton Odawara Resort & Spa - I found a high wall separating males and females.
On each side of the wall is a series of outdoor pools (an onsen can be inside or out) with water ranging from so-hot-it's-almost-scalding to tooth-chatteringly cold. You pick one you like - or move between them.
Sound advice at an onsen is to do what the Japanese do.
So, I strut confidently between pools - completely naked except for a small hand towel atop my head.
I return the next day, reminding myself to remember onsen etiquette and not make gaffes which would make a fool of me and horrify fellow-bathers.
Abide by these onsen customs to help you blend into the scene:
Dress: At a free-standing onsen, it's fine to turn up in street wear. But if the onsen is in your hotel and your room contains a bathrobe and slippers, arrive in these. [A hotel onsen charges guests less than non-guests. Hotels also often charge guests to use their swimming pools, which non-guests can use at a higher fee.]
Shower: These should be your first stop. Use plenty of soap. The objective is to become clean enough to share the baths with others. An Australian who often visits Japan and is an onsen aficionado tells me she avoids being typecast as an unclean foreigner by lathering furiously until after the last Japanese woman has left the changing room.
Towels: When it's time to soak yourself, don't wrap a towel around your waist. Instead, carry the tiny face towel you were given or drape it on your head - but don't use it as a modesty-enhancing fig leaf. Once in the bath (commonly the size of a family swimming pool), place your neatly-folded face towel on your head or at the edge of the pool near where you're wallowing. You can remove it from your head occasionally to mop your face, but don't rinse it in the water. [Towels, like swimwear, are regarded as potentially dirty.]
Nudity: On your walk from the changing room to the baths, you're completely naked. If this alarms you, you'd better not visit an onsen.
Tattoos: No, a girl with a (large) dragon tattoo won't be welcome. Tattoos are commonly associated with the yakuza, Japan's feared criminal network. An onsen may (or may not) make concessions, allowing "fashion tattoos". A little bird, butterfly, star, Chinese character or abstract design probably won't get you thrown out of an urban onsen. But an enormous dragon or tiger across your back will probably spark an attendant's polite invitation to leave. In the lobby of my hotel I bump into two irate Australian women, ejected because of big tattoos.
Soap: Despite being used liberally in the showers, soap mustn't enter the bath itself. Like swimwear, it's regarded as potentially polluting.
Conversation: Friends, workmates and family members chat between themselves, but it's not done to make small-talk with strangers. In a hot pool at Odawara I find myself in the company of a half-dozen men, each enjoying solitude. No one speaks. They're all deep in thought. For some reason, I'm reminded of hippos in the Zambezi. Out of the water, nods, smiles or slight bows are acceptable.
Adhering to etiquette will make onsen visits enjoyable. But flouting custom attracts disapproving stares.
IF YOU GO
Where to stay: Japan is well-supplied with hotels from ultra-opulent to bare-bones budget categories. For a glimpse of Japanese culture, stay at a ryokan (traditional inn); these are numerous in major cities as well as in rural destinations.
What to do: Globus Tours has a big range of tours and can tailor itineraries to accommodate specific interests.
Further information: See jnto.go.jp.
The writer was a guest of Globus Tours.
