'Sea' shells...

This is part of the Atlantic Wall, built by Canadian troops on Hankley Common, Surrey, durin WW2 to enable them to practice against the defences the Germans had constructed on the coast in France.
The holes pictured are from where the allied troops fired shells at the wall to determine how much fire power they would need to break through the fortified defences.
The wall is virtually as left 70 years ago, apart from a covering of moss and a few brambles around part of the base.