Yuyado Daichi in Yoroushi Onsen is ryokan in a remote area with not much else to do which is part of the appeal for me. I stayed in an "New building" river facing room which is newer than the main building (there's also an annex). The new building used to have its own smaller less used outdoor baths but looks like they may have been converted to maisonette guest rooms with private baths? All the communal baths were nice and I believe they're source fed. The outdoor baths by the river are probably the most known after the larger mixed gender bath which isn't common these days, especially in Hokkaido. They offer free optional cover-ups to women to use in the mixed bath. I remember the food being quite good. I imagine a winter visit would be gorgeous.

Recent video I found on YT. Turn on captions for English option.
If you're looking for a river side facing room as a solo, give this direct booking link a try for the New Building. I see a few nights in Feb still available which aren't appearing in the English booking page https://reserve.489ban.net/client/yo.../detail/960911 . Bookings for 2 or more people have more availability with more room options.