Before, I introduce onsen site in Japan.
I would like to teach you a few onsen terms.
Onsen（温泉) = Hot Springs
Ten Nen Onsen = Natural Hot Springs
Gen Sen Kakenagashi(源泉掛け流し) = Water comes directly from Source(Original Hot Springs)
Sentou(銭湯) = where you pay money to take a bath(have bath).
UchiYu(内湯) = Onsen in your Hotel(ryokan).
Sotoyu(外湯) = Onsen located out side of your Hotel(ryokan).
Uchi Buro (内風呂) = Bath Tub inside builing.
Roten Buro (露天風呂) = Bath Tub located outside of building. Usually without roof.
Super Sentou (スーパー銭湯) = where you pay money take bath, but they have more types of bath. Like Jet Bath. jacuzzi. Saunas are well known. They have more though.
Japanese Hot Spring - Foot Bath -
