Black plastic pond liner/ liner for a water feature. It has a plastic lid that covers the hole, so I assume you’d put a water pump underneath the lid for a decorative garden feature.
It was unrecognisable when we discovered it, all over grown with brambles.
But there was lots of shingle around it and the remainders of a pump nearby.
Pond / Water Feature (Ubley)
This offer has been gifted to some one and is no longer available.