Mow Cop 'Castle' as it's known, is, of course, a deliberate ruin. It was built to look like this, in a piece of eccentricity, by the local landowner in the mid eighteenth century.
The structure is placed right at the top of Mow Cop bluff and has views for miles for all around. It's quite a landmark.
In this picture I seem to have accidentally photographed (just to the right of the archway) some flying insect. Or could it be a bullet? Hmm.