This onsen hotel is located on the eastern side of Sakurajima. It is possible to stay in the hotel but my friend and I decided to soak up the volcanic minerals in the water one afternoon.
The onsen cost about 800 yen from memory and was a unisex onsen. However... every guest was provided with a white robe which was worn in the spa.
The bath location is gorgeous right next to the sea. There is a fesh water (cold) swimming pool next to the spa also which can be used in summer with a bathing suit.
Furusato is also a hotel which costs at least 13,000 yen per night, making it one of the most expensive in the area. The phone number is: 221-3111.