Nonaka Onsen is a lovely soak especially after hiking the nearby Mt. Meakan, a 4-5 hour hike where one can view the gushing volcano that heats the water for the baths below. The uchiburo is a treat: dark, water-soaked wood and near-scalding milky water. No shower nozzles or spigots, so you'll need to bathe by scooping a bit of the o-yu (bathwater) out and splashing yourself. Then hop in and prepare to go, "Aaaaaaaahhhh."
Outside, the rotenburo is small and much less hot, though not tepid. A comfortable soak, though the view is mainly of buildings and the privacy fence. Not much else.
Getting here is best with a rental car, though you could take a taxi from nearby Akanko Onsen, about 10 mins drive away.