Queen's Day in The Netherlands.
It's a national holiday (always on April 30th) to celebrate the birthday of the queen. There are flea markets in almost every city, music events, open-air parties & most people dress up in orange.
My Q-Day was in Rotterdam with some friends at the open-air party there. Although there were the craziest & cheapest-looking people around it was nice, sunny and very crowded & i met up with a good friend of mine i hadn't seen for a while :)