Each year, there is a cultural event in Europe, La Nuit des Musées, when for one Saturday night in mid-May participating museums throughout Europe are open free and late.
If you are in Europe in May it is an event definitely worth investigating, if not for the opportunity to enter museums free of charge then for the sheer experience of some of the world’s most famous museums after hours, surrounded by more locals than tourists. Another plus is that as part of the event, many of the museums have special events, such as concerts and guided tours. Attending, however, requires special planning. Paris, the city where I was located during their La Nuit des Musées, had 45 participating venues with 179 events. I utilized roughly the entire time span of the event, 6pm – 1am, and managed four venues.