The set up could be very similar to St Catherine's Fort/Island at Tenby,already dismissed on relative size/background issues.A landing jetty leads to steps behind one side of the rock formation,then onto a bridge and,incidentally,in Tenby's case to a gun emplacement surrounded by a stone wall(I think).
Attached is a slightly enhanced version-what is the general opinion of the pattern in the lower "girder like" component of the structure?
Regards
Roger