The Black Hill training bunker is pretty trashed on all sides - NN8303 : Bunker up close.
From inside, the gaping 'windows' help convey the horror for 'defenders' One hopes there were no defenders in this case!
I understand these walls and bunkers were built for training purposes in WW2. Troops were training for the D Day landings. It is reported that there is a concrete bombing target arrow in the area pointing towards the wall, which suggests that it was also used as a target for aircraft taking part in exercises.