The cave is real
That “abandoned, decaying cobblestone path” is fake, but it is neglected. The stones are fake are there is clearly an artificial underlay, like the whole path was delivered in a roll and they laid it all the way down to the crick.

Perfect to hide your Delorean under when time travelling!
I was thinking ‘Dark’ but same difference. Something timey wimey with that cave.
What does that sign say?
There are two signs mounted n there, warning about the dangers of cave collapse and saying this is a protected habitat for bats.
The path may be just a retaining wall built by laying quickcrete bags and watering them in place.
No there’s a layer of something rubbery/plasticy meant to hold the thing together. I guess it kind of prevents erosion but also is gross
The plastic is probably something like weed cloth, to prevent plants from overrunning the path



