"Onsen" is the Japanese word for the hot springs that can be found up and down the length of the country - from Okinawa in the south to Hokkaido in the north.
For the Japanese it is more than a popular pastime to soak in these natural thermal baths; it is a social activity, a health precaution, a time-honoured ritual, and a closely guarded facet of their cultural heritage. Though the thought may be daunting for most foreigners, bathing in an onsen is an unforgettable experience that no visitor to Japan should miss out on - which is why we've written this quick cheat sheet for first-time bathers.
From theme parks like Osaka Spa World to grand traditional institutions like Dogo Onsen; from giant baths carved from beaches and riverbeds to tiny city "sento" bathhouses - Japan has all manner of shapes and sizes of hot spring bath.
The good news is that the rules are the same wherever you go, so follow these instructions and you're guaranteed to avoid a faux pas:
1. Birthday suits only
This is the part that most foreigners find off-putting, but trust me - you'll feel much more embarrassed when you accidentally walk in with your swimsuit on! Naked bathing may seem scary to you and me but for the Japanese it's totally normal, and you'll soon relax when you see that nobody else is batting an eyelid.
2. Shower first, bathe after
Never, ever get into an onsen without first washing yourself thoroughly using the showers provided. This is to keep the water as clean and hygienic as possible for your fellow bathers, and you will not be looked on favourably if you break this golden rule. Small stools, bowls and toiletries are provided for this purpose, and you are expected to sit down while you wash to avoid splashing your neighbours.
3. Know your towels
Most onsen provide visitors with a set of towels (sometimes for a small fee), but smaller city bathhouses will expect you to bring your own. You will be given large towel for drying yourself, which should be left in the changing room with your clothes, and a small towel to be taken into the bath with you. You may use the small towel for washing under the shower and drying off excess water before you head back to the changing room, but never put it in the bathwater - most Japanese will put them on their heads while they soak.
4. No ducking
It is against onsen etiquette to submerge either your head or your hair in the water, so if you have long hair be sure to remember a hairband. This is to prevent strands of hair coming out in the bath, and to reduce the chance of spreading infection through the water.
5. No tattoos allowed
Unfortunately, tattoos are largely synonymous with organised crime in Japan, resulting in a blanket ban on body art across almost all onsen. If you have a small tattoo you will probably get away without anybody noticing, or you can choose to cover it with a sticking plaster or bandage.
If your tattoos are impossible to cover, you will sadly be barred from visiting most hot springs in Japan. This rule tends to affect more foreigners than it does criminals, but unfortunately tattoos are a taboo that runs deep in Japanese society and it'll be a long time before this changes. Your best chance to get the onsen experience in this case is to stay at a hotel that has private onsen baths, or visit a public hotel onsen late at night when all the other guests have gone to bed.
If you don't mind having gang members as your bathing companions, there are some bathhouses catering specifically to yakuza where tattoos are allowed, but it's not something we'd recommend!
6. Don't drink and bathe
Since bathing at high temperatures can leave you a little light-headed (and take it from us, Japanese onsen are HOT!), you are advised not to drink alcohol before visiting the baths. Surprisingly, drunkenness, slippery floors and hot hot water don't mix.
That said, a glass of wine or can of cold beer while you soak can be divine - so if you are lucky enough to have your own private onsen, enjoy in moderation!
And what if you really can't bear to bare?
For some people, the idea of public nudity really is an unassailable barrier to onsen enjoyment - but it doesn't mean that you have to miss out. Whilst most onsen are open to the public, it is also possible to rent hotel rooms with private outdoor hot spring baths, which can be a great compromise.
Another alternative is to visit an onsen with opaque water. It sounds silly, but many onsen in Japan have milky or muddy coloured water, so once you're submerged nobody can see a thing. Out of the water, you can use your small towel to preserve your modesty as you return to the changing rooms.