Seth Halleran
Google
This place is so incredibly rad. Different from a lot of the other onsens you'll find, this place is fairly rustic. You'll stop by the owner's home just off the road where you pay your (extremely reasonable) entrance fee (600yen for us). If you didn't bring a swimsuit and towel you can pay another 300 yen to rent both. From there you'll have to walk through a beautiful bamboo forest to get to the bathing area. Once there it is an incredible little oasis of hot springs with multiple baths, a cold waterfall, and steam room (its really a tent but it fits the vibe).
Anyway, extremely worth the bus ride, highly recommend.