A nuclear bunker made to house the government and civil servants in the event of nuclear attack is for sale.
The existence of the underground complex at Corsham, Wiltshire, was kept secret until recently, but the Ministry of Defence is now inviting buyers.
Built in the late 1950s, the bunker covers many acres and was decommissioned in the 1980s.
It is underground - more than 100ft (30m) down - and includes a kitchen and BBC studio.
The MoD says it has received hundreds of enquiries for purchase which will be under a private finance initiative, including two serious bids.
Despite being close to one of Britain's busiest railway lines, the facility was shrouded in secrecy for 50 years beneath non-descript government buildings.
Enormous and fully-equipped kitchens remain unused
In the 1950s as the threat of nuclear war intensified, the government pinned its hope for survival on buildings already used by the military.
If there had been an attack, the then prime minister Harold Macmillan and much of Whitehall would have been moved west to the bunker.
Nick McCamley, author of Secret Underground Cities, said in the past the government "simply refused to admit" the bunker existed.
"They gradually released documents about some of the other sites in the area, but as far as [this complex] was concerned it simply did not exist."
Chairs and office equipment are still stored there, in preparation for thousands of civil servants.
There are huge generators to provide power that might have been needed for weeks, boxes of paper and files, and enormous kitchens - all unused.
One of the largest telephone exchanges ever built would have linked to the regional government, which would also have been underground in the event of an attack.