(Photo of the Louvre via Konrad Kasior)
Once a year, museums all over Europe keep their doors open late, and for free. This is La Nuit Européenne des Musées, European Museum Night, and if you're in Paris this weekend you'd be a fool not to take advantage of this up-all-night culturefest (most museums are open until midnight, but some stay open 'til 2am). You can see the Venus de Milo at the Louvre, Marcel Proust's bedroom at Musée Carnavalet, the "Angels of the Odd" exhibit at Musée d'Orsay and many, many more exhibits and permanent collections all over Paris, for free. Here's a full list of the 166 events happening just in Paris.
La Nuit Européenne des Musées
Saturday, 18 May, 'til late