Over on the right is an iron gate that leads to a tunnel which then leads underground to a similar bunker. There were four total, laid out in a square.
This area I entered has train rails, probably for transporting the large guns and also ammo supplies, which lead into a heavily fortified bunker of concrete and earth. From inside this protected area, guns were pointed seaward to defend the shore from invasion.
I don't know if the spotter's building was to look out to sea (it seemed built too low to see over the berm), or to communicate with three other similar bunkers nearby.
The cannons were called "disappearing guns" and would rise up to shoot and then sink down behind the berm to not be seen from ships on the Atlantic. The idea was that it would be much harder to target them if they could not be seen.
The guns were never used in active defense of the Atlantic seaboard. For one thing, attackers never got close enough. Advancing technology eventually made the guns obsolete. They were replaced by ground to air missiles in the form of a Nike radar and missile installment. Those missiles were also made obsolete by the invention of ICBMs.
These are especially for Hans and others who dig the old military stuff!
I was shooting from under my umbrella by the way, juggling the DSLR in the right hand, umbrella handle clenched under the arm or in the left hand.