Every April 30, the Dutch celebrate the birthday of their Queen (though actually it's the birthday of the previous Queen, becuase the current Queen's birthday is in January, which is a less good time for a holiday.)

On Queensday, everyone wears orange and parties all day. There's also a national yard sale element, with people selling all sorts of junk on sidewalks and in parks. In Vondelpark, kids play music and set up carnival-type games. It's lots of fun.