What is superiority of Kurokawa Onsen?
Both the relaxed atmosphere and nature of the spring would be correct answers.
However, you should learn good lessons from this phoenix-like city, which changed from a ghost town just as same as many spa cities in the world, to one of the most popular hot springs in Japan.
Kyushu-Okinawa Region, Rating [5/5] Opaque, Private Bath, Sulfur Dioxide
Do you know real Arima Onsen?
Arima is counted among Thee Ancient Springs and is near big cities like Osaka and Kobe so some of you may have been there.
However, this historical spa city is facing depletion of the water; therefore, there are few inns providing real spring water that is not artificially processed.
Kinki Region, Rating [5/5] Extremely Hot, Lodging, Metallic Smell, Opaque