The hot spring water that gushes forth in the premises has never been in contact with outside air and flows directly into your bathtub.
The local source flows into a simple thermal hot spring rich in alkali. The source's temperature might be tepid, but take your time in the bath and you'll start feeling warm and fluffy inside.
These soft and calm waters will wash away fatigue, relief back and knee pain, and also make your skin smooth and pretty.

Festival of Nasu-Shiobara city in this month

Timeline of Direct source water: Hotaru Hot Spring