The BBC news site has revealed that a WWII bunker is up for sale. The Capel Battery site is on the cliffs at Capel-le-Ferne, Kent, overlooking the English Channel. The auction is due to take place in September and the guide price is £90,000-£100,000. (Source: Subterranean Exploration)
The site used to have several buildings on the surface but now all that remains is the battery and the tunnels below.
(Source: Battle Of Britain Memorial Org)
I found this YouTube video which presents a series of pictures of the sites construction in 1942.