Most were set down in 1940 as a network of barriers to thwart an expected invasion.
They pop up anywhere, in the middle of a field, behind a wall, or right on the edge of a cliff.
Now they are so intrinsically linked to the landscape they seem part of it, and yet all are a timely reminder of darker times.
On a walk between Abbotsbury and West Bexington on the Dorset coast, you can find some great examples.
Here plonked right on Chesil Beach is this proud pillbox.
With the whole of the South coast of England on the front-line it isn't particularly surprising to see one here.
And it's still in perfect condition, despite facing the full force of the weather for nearly 80 years.
The only thing that hasn't fully survived is the crafty disguise of a layer of stones to camouflage it, that blended it into its beach surroundings.
What is also interesting, is that as the pebbles on the beach have shifted, it has revealed the hidden base of the pillbox.
Not far from this is another one set in the middle of the hills that sweep down to the beach.
Oddly, its completely visible for miles around, built in red brick on a green field!
I can only presume it would have been covered in camouflage netting of some sort to disguise it?!
This stunning setting is just below St Catherine's Chapel at Abbotsbury, looking towards Weymouth and Portland. Below a pillbox still stands, and right in the middle of the picture, on the land jutting out into the Fleet near the Swannery, there is another one.
See if you can spot any on a walk sometime!