We would introduce what hot spring is, today.(In Wikipedia: The Free Encyclopedia. Retrieved from http://en.wikipedia.org/wiki/Onsen)
An onsen is a term for hot springs in the Japanese languages, though the term is often used to describe the bathing facilities and inns around the hot springs. Onsen were traditionally used as public bathing places and today play a central role in directing Japanese domestic tourism.
Onsen is not just for bathing facilities. It has various effect.