An onsen is a natural hot spring bath that is rich in beneficial minerals and is an integral part of Japanese culture. Onsen water is geothermally heated beneath the ground and rises to the surface bubbling hot. The prerequisites of an official onsen are that the water must contain at least one of the 19 designated chemical elements that naturally occur in hot spring water, and it must be at least 25°C when it comes out of the ground. Onsen baths can be beautiful objects in themselves, made from materials such as cypress wood, marble, and granite, and are often situated in areas of outstanding natural beauty or attached to traditional inns.
There are various types of onsen, including indoor bath tubs, big open-air bath tubs (known as a "rotenburo"), and places for washing, with complimentary soap and shampoo products for guests to use. Some onsen may also have additional facilities like a cool-water bath or a sauna.
Visitors to an onsen should follow certain rules and etiquette, such as washing thoroughly before entering the bath, not placing the head underwater, and not bringing glass inside the area. It is also important to note that most onsen in Japan do not allow entry to individuals with visible tattoos.
