Onnetto (an Ainu word) is a lovely name, and that goes for the lake as well. Not only is the lake beautiful in its own right, the youth hostel is also a hot springs - and one of those sulfury onsen that leave no doubt in your mind that it's a real mineral bath instead of reheated H20 (imitation onsen are rare, but they're not unheard-of).
As I recall, this is a photo of the aforementioned final hill up to the Onnetto Youth Hostel. Onnetto is worth the effort, though, as the next photo will show.