City Spa Tenku is Oita's most memorable urban bath: a hot-spring complex high in the JR Oita City building above the station. The baths sit on the upper floors, so you can soak while looking out over the city rather than hiding away in a backstreet sento.
It works well at the start or end of a day in Oita, especially if you want the onsen experience without making the trip to Beppu.