Shibaseki Onsen is one of Beppu's older municipal bathing areas, set away from the busiest hell-tour circuit. The draw is the ordinary ritual of the city: hot mineral water, simple baths, and the sense that Beppu's geothermal life is not only for sightseeing but for daily use.
It is a good choice if you want a more local soak after visiting the famous jigoku. Learn basic onsen etiquette before entering, bring your own towel, and check current hours because municipal baths can keep practical rather than tourist-friendly schedules.