I soon found the curvy path. It was lovely! Would make a great morning running route. And I got to the bridge. I walked to the house again. Didn't see much I hadn't seen before, so I went back to the bridge, crossed it, and followed the straight path back to the road (with an extra excursion to the closest you can legally get to the house on the other side of the river). Nice!
Potential running route?
The other side of the river: the black car is parked next to the neighbour's house
I did wonder, though, what that river would do on a wet day. Googling 'flooding Bethesda' didn't bring up anything untowards. And Natural Resources Wales does indicate a flood risk but it doesn't seem excessive. I might have to knock on the neighbours' door to ask them about it! The past few years have seen some atrocious weather; if it hasn't flooded then it is not likely to flood too often. I'm dreaming again...
House where the black star is. From https://naturalresources.wales/evidence-and-data/maps/long-term-flood-risk/?lang=en