When I arrived in Kusatsu I was immediately drawn to the little, historical Japanese town. It had charming traditional wooden buildings which surrounding the hot springs or onsen. The waters were neon yellow-green and the clouds of steam rising on a cold, sunny, winter day gave the aura of otherworldly-ness. The onsen waters were calming, serene, healing and of course soothingly hot. I went from one to another and it was better than any spa.
Japan is a volcanically active country and has thousands of geothermally heated onsen. The waters are rich with minerals such as sulphur, sodium chloride, hydrogen carbonate and iron. The water temperatures can reach 100-110⁰ !
If you can visit only one place, a visit to Kusatsu is required to experience the mysterious and ethereal waters of the onsen—definitely my favorite place in Japan.