This WWII pill box bunker is on the banks of the Thames, somewhere near Goring. The bunkers are apparently too difficult to demolish – which I guess is their point. The owners of this one seem to have decided to incorporate the left-over military installation into some landscape design. Note how the dry stone walling (incorporating planting features) provides a textured plinth, and how planting has been introduced over the top of the bunker. The statuette birdbath might be regarded by some as a step too far.
Landscape follies often summon historical imagery, and sometimes simulate some kind of destruction in the form of ruination. Here, the history is real, and the destruction a possibility averted by the Battle of Britain and the Russian front.
Alternatively it could be deep-cover camouflage. Which reminds me to dig out a photograph of a WWII faux gothic revival machine gun emplacement addition to the Houses of Parliament.