Every first Thursday of the month, the Museum of Fine Arts (MSK) in Ghent, stays open late until 10pm. The oldest museum in Belgium (even older than the actual country!) is of course worth a visit any day of the week, but on late Thursdays you get to enjoy some fun and unique experiences on top of the usual art collection.
For example, when I last visited during a late Thursday, they had organised a live drawing event and collaborated with Ghent cocktail bar The Cobbler, who created two signature cocktails inspired by the temporary exhibition on Erich Heckel. A very 'Ghent' experience :)