This is the entrance to the Cabinet War Rooms, where Winston Churchill and his cabinet spent much of the war. Part of a larger complex which runs beneath much of Whitehall, the rooms were the heart of Government during the Blitz, and it was here that many of the decisions which led to eventual victory were taken.
Churchill and his family and private staff lived down here for long periods of time and had their own suite of nine rooms, now called the Churchill Suite, and Churchill famously had a special telephone scrambler system with which he spoke directly to President Roosevelt disguised as the Prime Minister's lavatory.
The underground complex was designed with the prospect of widescale bombings of London in mind and is covered by a thick layer of concrete up to three metres thick.
The war rooms are interesting, but are almost eclipsed by the Churchill Museum which also shares the site. This gives a fascinating insight into the life of the man himself.
The price is a little steep at £12.95 a head, but worth it in your author's opinon for the combination of two museums and the insight into the subterranean lives of the war time leadership.
For more information visit the website at http://cwr.iwm.org.uk/.
Click here to see the location on a map.
*Edit* - IanVisits raises the prospect of visiting another, less well known, subterranean London War Cabinet bunker here (full details here).