What you see in this photo are actually 2 distinct military sites.
The mound behind is a World War II decoy centre, used to coordinate a mock up of Falmouth Docks that was set up off Nare Head to fool German night bombers.
In the foreground there are 3 metal objects. These are actually the external features of a Cold War nuclear bunker. 12 feet below the surface is the preserved bunker, which is occasionally open to visitors