Old Pillbox

Apparently about 28,000 pill boxes were built during WWII for use in the event of a German invasion. It is thought about 6,500 still remain.  We have lots in Kent. The extra is a map I found on the internet copied from Henry Wills "Pillboxes"  showing the Kent pillboxes.   Our 4 mile walk around Fordcombe today took  us along a stretch of the Medway which has loads of these defences and we spent some time imagining soldiers on shallow boats paddling up the river.  I have marked the map in extras with this pillbox which I liked because it was not covered in brambles unlike so many round here. 
I think it qualifies for Derelict Sunday which I seem to think I can add on any day of the week but am not sure which tag to use.