National Gallery

After war broke out, and with invasion expected in 1940, the National Gallery's pictures were sent away from London. By the summer of 1941 they were hidden in a slate mine in the mountains of North Wales. Someone had suggested shipping them to Canada, and Churchill answered: hide them in caves and cellars, but not one picture shall leave this island. Deep in the Manod quarry, in brick chambers built to keep humidity and temperature stable, van Eyck's Arnolfini Portrait and Turner's Fighting Temeraire waited out the Blitz while the pianist Myra Hess gave lunchtime concerts in the emptied galleries back in London.

The gallery had always belonged to the public rather than a palace. It began in 1824, when Parliament bought 38 paintings from the banker John Julius Angerstein, and it was planted deliberately at Trafalgar Square, in the centre of London, so that a clerk or a carter could reach it as easily as a lord. Its permanent collection remains free to enter.

Through the war the staff kept bringing single masterpieces back from Wales, one at a time, to hang in the bare building as a Picture of the Month for a city under bombing. The same rooms today hold the Wilton Diptych, Van Gogh's Sunflowers and Constable's Hay Wain, open to anyone who walks up the steps from the square.