三原山温泉
(みはらやまおんせん)
Mihara-yama Onsen Onsen and hotel on the way to the volcano in Oshima, 800 yen. Water 40 degrees, brownish but clear, no smell. The view from the outdoor bath is amazing — you can cool off in the wind and there are places to sit. Indoor bath same temperature. Reachable by public transport only on weekends and holidays — I walked, of course. They serve local milk in a proper carton (but not glass bottles). Like, overall a good onsen with a view.