Nestled on either side of a steep gorge about one hour northeast of Aso town, tranquil Kurokawa Onsen (黒川温泉) is one of Japan's prettiest hot-spring villages and has won top onsen honours several years in a row. Safely secluded from the rest of the world, it's the perfect spot to experience what an onsen ryokan getaway is all about.
For day-trippers, a nyūtō tegata (onsen passport; ¥1300) allows access to three baths from Kurokawa's 24 ryokan (open 8.30am to 9pm). Buy one at the tourist information desk and ask which locations are open during your visit. The office even has an official onsen sommelier!
Favourite baths include Yamamizuki, Kurokawa-sō and Shimmei-kan, with cave baths and riverside rotemburo (Kurokawa is especially famous for its rotemburo). Many places offer konyoku (mixed bathing).