Buses run from Yufuin and it was a short 1 hour ride. Kurokawa Onsen is also connected to Mt Aso and Kumamoto Take the Odan Bus (Direction Beppu towards Kumamoto). Click here for the timetable.
As the name suggests, Kurokawa Onsen is best known for natural outdoor hot springs called rotenburo. The thing to do is to grab a nyuto tegata (hot spring pass), put on your yukata, and go onsen hopping. The hot spring pass costs 1200 yen and gives you access to 3 hot springs (valid for 6 mths). You could pick it up at your ryokan or at the Kurokawa Spa Hotel Association Information Center. More on my picks soon.
The little town could be explored in your Japanese slippers. Enjoy the natural forested landscape complete with little wooden houses, stone stairs and flowing river.
There are many ryokans in Kurokawa Onsen and each comes with their own hot spring baths. A ryokan stay with half board option is a must. We stayed at Wakaba Ryokan and paid 31500Y for 2 pax per night (breakfast and kaiseki dinner included). Our ryokan was alright in my opinion but not super fantastic. The baths are so so only.
My first option was Ryokan Sanga, which comes highly recommended, but as usual we booked too late. Another ryokan that i liked is Ikoi Ryokan, which is just beside Wakaba. Both ryokans are a stairway down from the busstop which makes them really convenient. Ikoi has some really fantastic onsen baths which we visited using our onsen pass. Love!
My tip for Kurokawa Onsen is to head there early, start onsen hopping and then spend the night in the lovely town. We even took a short run around the place and saw some big hotels (don't stay there please). It's a good way to break up the traveling from Yufuin to Mount Aso if you're planning to head there.
Can't wait for my upcoming onsen trip to Nagano this year end! What's your favorite onsen spot in Japan?