Aso City is renowned for its top-quality hot springs with abundant water. Among the hot springs, Uchinomaki Onsen is the representative of the hot springs in Aso, where over 30 hotels and Japanese-style hotels are located. 

Quote : https://kumanago.jp

HOW TO ENJOY A JAPANESE STYLE PUBLIC BATH 

A hot spring town spreads along the Manganji River. There are three lodging facilities. There are 3 public baths. Manganji Onsenkan, an open-air bath (kawayu) along the river, and a hot spring located 100m upstream of this river. Kamiyu became a men-only bath when the Manganji Onsenkan was rebuilt.

Jigoku Onsen is a hot spring located in Kawayo, Minamiaso-mura, Aso-gun, Kumamoto Prefecture. The name of the hot spring is derived from the fact that there is a place where there is no vegetation (so-called hell) due to the volcanic gas eruption on the back of the hot spring.

https://ja.wikipedia.org/wiki/%E5%9C%B0%E7%8D%84%E6%B8%A9%E6%B3%89