The Nuit des Musées is an initiative launched by the French Department of Culture in 1999. Each spring (in 2010, 15 may), the museums of Paris, and the rest of the EU till 2001, stay open until 1 AM and entrance is free. It also boasts performance art and other happenings. Several museums, including the Louvre, will open their doors for free this Saturday, so don’t miss out.