Kareigawa no Yu is a lovely higaeri (day-use) only bath that is a bit out of the way but is new, clean, stylish, and tucked right next to the historic Amori River. Baths are beautiful constructed and look out on a peaceful stretch of rocks and water; the more expensive rooms even have rotenburo. As with many kazoku (family) style baths, you add the water yourself when you enter and can make it as hot or cold as you please.
You'll need a car or taxi to get here, unfortunately, as it's a bit out of the way. But those willing to make the trip will be rewarded with a place that seems as quiet, contemplative, and peaceful as some of the high-mountain onsen spots, despite the fact that this is essentially in the suburbs.