What Exactly is a Natural Hot Springs Bath "Onsen"?

An onsen is a Japanese hot spring. Many are used as hot springs baths. Although most hot springs baths are developed inside, many hot springs baths also have an outdoor bath known as a rotenburo or notenburo (also called open-air hot springs bath). Baths may be publicly run by a municipality or privately run by a local ryokan.
Traditionally, men and women bathed together at the onsen, but now most onsen are only for single-sex bathing. Onsen are often found in the countryside and are a tourist attraction.

Outside (Open-air) Onsen Image

Onsen are also a very common feature to ryokan (traditional Japanese inns), which serve the same traditional purpose of relaxing the body from the fatigue of travel. Japanese often talk of the virtues of "naked communion" for breaking down barriers and getting to know people in the relaxed atmosphere. Traditionally, onsen were located outdoors, and by definition use naturally hot water from geothermally-heated springs. Onsen baths are different from "sento," indoor public bath houses in the city where the baths are filled with heated tap water. Major onsen resort hotels often feature a wide variety of themed spa baths and artificial waterfalls in the bathing area.

Inside Onsen Image

Onsen water is believed to have healing powers derived from its mineral content. A particular onsen may feature several different baths, each with water featuring a different mineral composition. The outdoor bath tubs are most often made from Japanese cypress, marble or granite, while indoor tubs may be made with tile, acrylic or stainless steel.

Some features found in ryokan today are ryokan rooms which have their own private open-air hot spring bath, which are not only a luxury, but one of the best ways in Japan to get away from the hectic life of the city.