I started to digging in a spot to plant a shrub, when I struck stone! Beneath 10 cm of bush litter I exposed a long covered pathway. And with a bit more digging of another sort, I found a photograph of the original pathway. See photos 'now and then' below. The bridges have disappeared, as has the waterway or pond that presumably flowed under it.
I also a discovered a rock retaining wall along the edge of the property just beyond these photos.