An onsen (温泉) is a Japanese hot spring and the bathing facilities and inns frequently situated around them. As a volcanically active country, Japan has thousands of onsens scattered throughout its length and breadth. Onsens were traditionally used as public bathing places and today play a central role in directing Japanese domestic tourism.

Onsens come in many types and shapes, including outdoor and indoor baths. Baths may be either publicly run by a municipality or privately often as part of a hotel, Ryokan, or bed and breakfast (民宿 minshuku).

Onsens are a central feature of Japanese tourism, typically found out in the countryside, but there are a number of popular establishments still found within major cities. They are a major tourist attraction drawing Japanese couples, families, or company groups who want to get away from the hectic life of the city to relax. Japanese often talk of the virtues of "naked communion" (裸の付き合い hadaka no tsukiai) for breaking down barriers and getting to know people in the relaxed homey atmosphere of a ryokan with an attached onsen. Japanese television channels often feature special programs about local onsens.

The presence of an onsen is often indicated on signs and maps by the symbol ♨ or the kanji  (yu, meaning "hot water"). 

Indoor onsen - Ofuka Onsen

Traditionally, onsens were located out of doors, although a large number of inns have now built indoor bathing facilities as well. Onsens by definition use naturally hot water from geothermally heated springs.


Onsens are different from sentō, which are indoor public bath houses where the baths are filled with heated tap water.

The legal definition of an onsen includes the requirement that its water must contain at least one of 19 designated chemical elements, including such minerals as iron, sulfur, and metabolic acid, and be 25 °C or warmer before being reheated. Stratifications exist for waters of different temperatures.

Major onsen resort hotels often feature a wide variety of themed spa baths and artificial waterfalls in the bathing area utaseyu (たせ湯).

Onsen water is believed to have healing powers derived from its mineral content. A particular onsen may feature several different baths, each with water with a different mineral composition. The outdoor bath tubs are most often made from Japanese cypress, marble orgranite, while indoor tubs may be made with tile, acrylic glass or stainless steel. Particular onsens may also promote the special mineral composition of their waters, together with the healing properties these may have.


At Onsens, various other services, such as massages, may also be offered.


Mixed bathing

Guidebook to Hakone from 1811

Traditionally, men and women bathed together at both onsens and sentōs but gender separation has been enforced since the opening of Japan to the West. However this still persists at some special onsen in rural areas of Japan, which usually provide the option of separate "women-only" baths or different hours for the two sexes. Men may cover themselves with a small towel while out of the water, while women usually wrap their bodies in full-size towels. Children of either sex may be seen in both the men's and the women's baths. In some prefectures of Japan, including Tokyo, where nude mixed bathing is banned, people are required to wear swimsuits or yugi (湯着), which are specifically designed for bathing.

Onsen Etiquette

Baskets

Ensuring cleanliness

At an onsen, or a sentō, all guests are expected to wash their bodies and rinse themselves thoroughly before entering the hot water. Bathing stations are equipped with stools, faucets, wooden buckets, and toiletries such as soap and shampoo; nearly all onsen also provide removable shower heads for bathing convenience. Entering the onsen while still dirty or with traces of soap on the body is socially unacceptable.

Swimsuits

Bathers are not normally allowed to wear swimsuits in the baths. However, some modern onsen with more of a waterpark atmosphere require their guests to wear a swimming suit in their mixed baths.

Towels

Onsen guests generally bring a small towel with them to use as a wash cloth. The towel can also provide a modicum of modesty when walking between the washing area and the baths. Some onsen allow one to wear the towel into the baths, while others have posted signs prohibiting this, saying that it makes it harder to clean the bath. It is sometimes against the rules to immerse or dip towels in the onsen bath water, since this can be considered unclean. In this latter case, people normally set their towels off to the side of the water when enjoying the baths, or place their folded towels on top of their heads.

Noise

Onsen vary from quiet to noisy; some play piped music and often feature gushing fountains. Bathers will engage in conversation in this relaxed situation. There are usually prohibitions against rowdiness in the washing and bathing areas. A small amount of excess energy and splashing around is usually tolerated from children, however.

Shower cubicles

Tattoos

Around half of onsen operators ban bathers with tattoos from using their facilities. The original reason for the tattoo ban was to keep out organised gangs such as Yakuza and members of other crime gangs who traditionally have elaborate full-body decoration.

Tattoo-friendly onsen do exist. A study by the Japan National Tourism Organisation found that more than 30% of onsen operators at hotels and inns across the country will not turn someone with a tattoo away; another 13% said they would grant access to a tattooed guest under certain conditions, such as having the tattoo covered up.

With the increase in foreign customers due to growing tourism, some onsens that previously banned tattoos are loosening their rules to allow guests with small tattoos to enter, provided they cover their tattoos with a patch or sticking plaster.

Onsen Therapy

The volcanic nature of Japan provides plenty of springs. When the onsen's water contains distinctive minerals or chemicals, the onsen establishments typically display what type of water it is.

Some examples of types of onsen include:

  • Sulphur onsen (硫黄泉 iō-sen)
  • Sodium chloride onsen (ナトリウム泉 natoriumu-sen)
  • Hydrogen carbonate onsen (炭酸泉 tansan-sen)
  • Iron onsen (鉄泉 tetsu-sen)

In Japan, it is said onsen have various medical effects. Japanese people believe that a good soak in proper onsen heals aches, pains and diseases, and visit onsen as part of the treatment for such ailments as arthralgia, chronic skin diseases, diabetes, constipation, menstrual disorders, and so on.

These medical benefits have given onsens a central role in balneotherapy which is called "Onsen Therapy" (温泉療法 onsen-ryōhō). Onsen Therapy is a comprehensive bathing treatment conducted to maintain health, normalize dysfunctions, and prevent illness.

With thanks to Wikipedia