The volcanic island that it is, onsen (natural hot springs) are found in many places throughout Japan. The water that coming up through the rocks in each region differs so much in color, nutrients, and even texture that no one onsen is ever quiet the same. For centuries the Japanese have been using this natural hot water to bathe, and tales of the healing power of the onsen, rich in nutrients and minerals, are aplenty.
Depending on where you’re from, the idea of bathing naked with strangers may seem a little intimidating, especially in a country where correct etiquette is so rigorously defined. But overcome these initial inhibitions and you will discover a culture of communal bathing that runs deep in Japan’s history.
There are three ways to experience communal bathing in Japan.
Ryokan (Japanese inns) are typically found in the onsen regions of Japan. They are peaceful establishments—retreats might be more apt—where guests go to relax and enjoy Japanese omotenashi (hospitality). The ryokan in these onsen regions provided communal bathing facilities for guests into which the natural spring water of the region flows. For more information on ryokan see here. For more information on ryokan see here.
Day onsen are onsen facilities that do not offer overnight accommodation. Because they are dedicated hot springs, the bathing area (and thus the number and variety of baths) is usually far greater than the Japanese inns, which are only catering for staying guests. Prices vary from ¥500 to ¥2,500 and each one is unique, not least because the natural water varies drastically between regions. In Tokyo, a coffee-coloured spring water which turns a jet-black in the baths is very common, as is water with a light-amber colour. For more information on day onsen see here.
Sento are public baths which do not use natural spring water—whereas the onsen are for pleasure and relaxation, the sento exist to serve a more practical need. Indeed, the two kanji that make up the word sento (銭湯) mean “hot water” and “money”; in other words, you are simply buying hot water. This was especially true during the post-war decades when it was not common for a house to have its own bath tub. The vending machines selling milk that are often found outside the changing rooms in the onsen and sento are a legacy from times when most households didn’t have the luxury of a refrigerator, either.
The sento are much cheaper than the day onsen (¥200-300). And while you won’t get to relax in the jet-baths, salt saunas, and indulge in the other services, a visit to a sento will give you an altogether more local sense of everyday Japan.
For information on etiquette and how to use the onsen see here.