Number 5: Shima Onsen
Shima Onsen (四万温泉, lit. "Forty-thousand Hot Spring") is a sleepy hot spring town in the northwest mountains of Gunma Prefecture. Considered among the top four hot spring towns in the prefecture (alongside Kusatsu, Minakami and Ikaho), Shima Onsen is also thought to be one of the oldest in Japan. It is so named because it was once said that bathing in its abundant spring waters could heal as many ailments as its name implies.