After seeing the cliff again, I headed up the pass... and immediately hit the fog that the YH people had promised. The top was completely socked in; no views at all. So I sped down the other side and, a few kilometers outside the town of Rausu, I happened on something even better: a free open-air onsen by the riverside. This photo was taken from the road; you can just make out the small hut (provided for changing clothes and also to house the women-only secluded section); the communal open-air bath is just to the left of that. There were only men in that bath, mostly local fishermen.
Here’s a photo of the bath itself, taken by one of the people I’d met at the YH who happened to come here at the same time. It was the perfect way to end a trip - and it was the reason that, when I got to Rausu and found everything socked in with fog even at sea level, I scuttled plans to cycle 20 km up the coast. No point; my objective had been to check out a great onsen, and I’d already been to one.