Foreign and Commonwealth Office, King Charles Street, London

One of the hundreds of properties around London that open their doors for one weekend a year, the Foreign and Commonwealth Office is a heavily-restored throwback to the mid-nineteenth century. The grandeur of the British Empire lingers on in its ornate meeting rooms, stately staircases and the marble splendour of Durbar Court - a covered courtyard ringed by balconies with beautifully-tiled floors and intricate plasterwork. The lavish India Office and the golden Locarno Suite, with its ostentatious arched ceilings, are still in use as offices or meeting rooms. One of the highlights is the Grand Staircase with its bronze bust of Anthony Eden, heroic neo-classical paintings and massive golden chandeliers. But all this extravagance is somewhat offset by the mundane reminders, such as the plastic water dispensers and waste paper bins, that this building has to earn its keep in the cash-strapped public sector. On Open House weekend, admission is free and the friendly security guards make you feel very welcome. 7/10