RAF Colerne
Not purely related to aviation, but I understand that the area immediately adjacent to RAF Colerne is, like others in the area, an underground facility of a size of a small city. There is a maze of corridors, and its own disguised railway system which enters the facility through steel doors. I also understand that anyone stopping on the adjacent lanes for a look round will soon be moved on by Mod police, or a security firm. I cannot verify this; my only experience is of having been on an official visit to another location in that area, over 40 years ago. What an experience! Almost anything could be stored in such places...and probably was.