natural hot spring
Refers to a hot spring whose water is naturally heated by geothermal activity, as opposed to an artificially heated bath. Often used in travel and onsen facility descriptions.
This inn draws water from a natural hot spring.
The minerals in natural hot spring water are said to be good for the skin.
I relaxed by bathing in the inn's natural hot spring.
I booked a hotel with a natural hot spring.
This hotel drilled its own natural hot spring.