Koninginnedag (Queen's Day) is an official holiday in the Netherlands, It is supposed to be the Queen's birthday, but it is celebrated on 30 April, no matter when the Queen's birthday is, and the Queen doesn't necessarily celebrate it, because there are effigies and epithets and it's more pleasant without her.
On Koninginnedag, all the streets in the Netherlands are empty. Not even cabs and ambulances are allowed onto the streets. This is because, just after the Liberation, the streets were empty as well, for all the Belgians had fled to their distant homeland. (The Muslims had not yet arrived.) The lack of mass transit forces everyone in the Netherlands to stay home all day. They are mostly glad when it rains on Koninginnedag, because the rain might have kept them indoors anyway. Alas, most Koninginnedagen are nice and sunny.
Although many Dutch find it unpleasant to stay at home, happily, the tax collectors stay at home as well. Thus, many of the resourceful but flinty Dutch rush out to cram their tiny front yards with used crap and try to sell it, tax-free, to anyone who walks by. This tradition is called the vrijmarkt (free-market). Favorite Dutch pastimes on this day are claiming they actually like the free market, and pretending they are too sophisticated to care about automobiles.
Koninginnedag was started to commemorate the year 1703, in which, on the Queen's birthday, the Dutch killed Belgians for no reason. Killing Belgians is no longer an obligatory part of the celebration. However, the day after Koninginnedag, Dutch children like to pretend it is still Koninginnedag, because this means they can still murder Belgians and Germans without any other excuse.
Some Belgians who survived the mass slaughter still roam the streets. Dutch hunting parties track them down at night and smoke pot while burning their corpses. Sometimes the Germans come as well, simply to savor the smell of burning corpses.