This scenic mountain onsen town is famous for its "healing" waters, steamed sweets ("manju"), and a really interesting central area called the "Hot Water Field" (湯畑) where the scalding, sulfurous water is collected and funneled off to the various inns, baths, and ryokans. Doable in a day trip from Tokyo, Kusatsu is best done as an overnight or a relaxing weekend if you want to have time to really soak in the surroundings. If time permits, try to catch one of the dance-like performances where the water is cooled with long wooden paddles until it no longer scalds. There's a nice, very popular public bath right next to the Yubatake, as well as an older, venerable bath called Otaki no Yu which has baths of different kinds of Kusatsu Onsen water, letting you try the various kinds as you soak. It also alternates male/female hours so both sexes can visit all areas of the bath, so check first before entering.
Kusatsu can be easily reached by taking the train as far as Takasaki, then getting a bus from there to Kusatsu Onsen. It will drop you off a few minutes' walk from the Yubatake, where you'll be able to take pictures and find a prime spot to soak. Those with more time on their hands (or those staying overnight) may want to opt for an early morning dip as the baths may be less crowded. Photo takers might also appreciate the early morning hours.
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