There are secret chambers all around. In cornwall, one of the locals found a tunnel in his house that went to the sea, old smugglers tunnel. Even had a rusty old flintlock on the floor.
My great grandfather lived in Knowle, bristol, in an area that used to be a farm. When they knocked down buildings to build houses, they didn't bother sorting out some of the old tunnels etc. He used to tell a story about the big barn near his house, which had a deep cellar. Apparently they put concrete blocks down at ground level, leaving the actual cellar intact, and then just put turf over the lot of it. The upshot being that one of the guys (I like to point the house out when I'm up that way) only has to dig a bit of turf up in his garden and he's got access to a massive underground chamber.