One of a row of air-raid shelters at Hardwick House, Whitchurch, near Reading, UK (here on Google Maps). When I first walked past them, several years ago, I didn't realize there was more than one; maybe they were more overgrown then. Actually, there are four in a line parallel to the Whitchurch-to-Mapledurham track. Here I suggested that they might have been a starfish site, but I now think that is wrong and it is more likely that they were air-raid shelters for people living or working at the House. Maybe Hardwick House was occupied by a branch of the government or the military during the war? Does anyone know?
All four shelters are identical in layout and construction. Each has a little closet (a toilet?) next to the entrance door. Each main room originally had a circular skylight with a metal ladder to it, though the westernmost one's ladder has been detached. I understand that these skylights were emergency exits for use in case the main entrance was blocked by bomb damage. The main rooms seem to be particularly, even unnecessarily, roomy.