Isabella Stewart Gardner Museum

In the early hours of 18 March 1990, two men in stolen police uniforms talked their way into this Boston museum, tied up the guards, and over 81 minutes cut 13 works out of their frames, among them Vermeer's The Concert and Rembrandt's only seascape, the Storm on the Sea of Galilee. It remains the largest unsolved art theft in history, and the reward now stands at ten million dollars.

The empty frames still hang on the walls. That is down to Isabella Stewart Gardner herself, a Boston collector who built the place as a Venetian palazzo around a glass-roofed courtyard and opened it in 1903 as Fenway Court. Her will fixed the arrangement of every room forever, so nothing can be moved or replaced, not even to fill a gap left by thieves.

What remains is still extraordinary, Titian's Europa, a Botticelli, and rooms crowded exactly as she left them, with flowers still grown in the courtyard to her plan.