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 all of its major islands.
Onsens come in many types and shapes, including outdoor (露天風呂 or 野天風呂, roten-buro or noten-buro) and indoor baths. Baths may be either publicly run by a municipality or privately (内湯, uchiyu), often as part of a hotel, ryokan, or bed and breakfast (民宿, minshuku).
The presence of an onsen is often indicated on signs and maps by the symbol ♨ or the kanji 湯 (yu, meaning “hot water”). Sometimes the simpler hiragana character ゆ (yu), understandable to younger children, is used.
Traditionally, onsens were located outdoors, 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, indoor public bath houses where the baths are filled with heated tap water.
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