Each September, up to 5,000 of the most amazing pieces of British architecture, engineering and heritage are opened up to the public.
The main event and the focus of the series is the London Open House architecture event, which offers the chance to visit some very special buildings, many of which are usually closed to the public. From the Bank of England to a top secret Second World War bunker used by Churchill; Gladstones St Deiniols library in Wales to the cutting edge life-saving research laboratories at Queen Marys university. Its a once in a year opportunity to go Behind Closed Doors...