A couple places like that that I can think of in eastern Jpn are Ikaho Onsen and Ginzan Onsen. But if you're staying 2 nights and you want to browse around town a bit on your one full day there, then there's not that much in town.

In Jpn, you have onsen ryokans in serene settings or self-contained onsen resorts in isolated areas where you're not going to leave the grounds from check-in till check-out, then you have ryokans in onsen towns where you might go out for walks. In the latter category, you'll find that most major onsen towns have lots of concrete high-rises. Kusatsu, Hakone Yumoto, Echigo Yuzawa, Gero, Arima, Kinugawa, Noboribetsu, etc, etc. That may not be what you're looking for. But if you're going to spend 2 onsen nights in the vicinity of Tokyo, I highly recommend Kusatsu.

Kusatsu is the most quintessential onsen town that I can think of. The town is pretty vibrant and fun to walk through, with a fair amount of shops and a large hot spring in the middle of town. The onsen water quality is top-notch (this is increasingly important as you become more of an onsen snob). Yes there's plenty of concrete in town, but you're spending most of your time within the confines of your ryokan anyways.