Geograph - photograph every grid square

The square of concrete is the top of an old cube, but one of a line of such blocks that stretched all the way down the dunes and beaches of Northumberland. Together with masses of rusting barbed wire and larger concrete machine gun bunkers (we called them pill boxes) they still lined the beach when I first visited in the 1950s. A dangerous place for kids and adults to play.

There's a largely untold story about the construction of all these defences, and the many airfields that sprang up along the east and south coasts.