The plan worked and we took sandwiches with us for lunch, drove to Penrhyndeudraeth and parked in the main car park. From there we walked behind the town along lanes and tracks we'd never explored before. There was a certain amount of wandering along very muddy tracks through some woods before we discovered that a clearly marked track on the map no longer existed in reality.
So we retraced out footsteps a little way and tried again, this time finding a narrow lane that ran alongside some lovely rock outcrops that will be much better than sending people to flounder through trackless forest.
This was at a point where the path was actually visible.
Round about the point we turned back, there was this picturesquely ruined barn.
We came back along a path running along the top of what was obviously an artificial dyke. From here there were some views that, in decent light, would be very photogenic, so I have made a note to self to return on a day that isn't just gloomy and totally overcast.