This is an app that allows you to search for about 7,000 hot springs in Japan.

In Japan, onsen (温泉) are the country's hot springs and the bathing facilities and traditional inns 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 (内湯, uchiyu). 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).

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.
Indoor onsen at Asamushi Onsen

Traditionally, onsens were located outdoors, although many inns have now built indoor bathing facilities as well. Nowadays, as most households have their own bath, the number of traditional public baths has decreased, but the number of sightseeing hot spring towns has increased (most notable ones including Kinosaki Onsen, Togura Kamiyamada Onsen, and Akanko Onsen). Onsens by definition use naturally hot water from geothermally heated springs.