Deep in the sandstone hill at Drakelow near Kidderminster, 5km of tunnels were dug in 1942 to house a hidden factory.
The Rover company was building parts for radial aero engines and its plants in Birmingham and Coventry were very vulnerable to air raids.
Over 26,000 square metres of underground floor space housed machine tools, heat treatment gear, laboratories, store rooms, offices, a canteen, a dining room and games rooms.
In the 1960s the threat was different - the cold war. Drakelow was refurbished as a Regional Seat of Government - a nuclear bunker designed to help control the population of the Midlands in the aftermath of a holocaust.
It had its own independent water supply, generator, air conditioning and air filters. There were male and female dormitories, a sick bay with operating theatre, offices and BBC radio studios.
This role lasted in various forms until 1993, when the site was removed from the secret list and sold off.
This recording shows an exploration of the whole complex, starting in the Rover factory area with remains such as the original blast doors, time office, an electric truck, the battery room, a laboratory and the massive ventilation fan.
The 1960s period is represented by a canteen, dormitories, offices and a BBC studio.
The 1980s-90s relics include shower rooms, the generator hall and the fallout decontamination facility, together with another BBC studio and a kitchen with its stainless steel equipment virtually unused.
The images on this page are taken from the video.