what is an onsen

An onsen is a natural hot spring bath that is geothermically heated underground by the volcanic activity of the land. In Japan, onsen refers to both the hot spring itself and the accompanying facilities, which are often part of a hotel, resort, or traditional Japanese inn called a "ryokan". There are approximately 25,000 hot spring sources throughout Japan, and approximately 3,000 onsen establishments use naturally hot water from these geothermally heated springs. Onsen may be either outdoor baths (roten-buro / noten-buro) or indoor baths (uchiyu) . Traditionally, onsen were located outdoors, although many inns have now built indoor bathing facilities as well. Onsen water is believed to have a multitude of healing properties and is rich in beneficial minerals. To enter an onsen, visitors must follow certain etiquette rules, such as washing thoroughly before entering the bath and not placing the head underwater.