Today is Queensday in Amsterdam, it is also known as Koninginnedag. Queensday is a national holiday in the Netherlands. It is to celebrate the birthday of Queen Juliana, which was actually tomorrow - but celebrated today. The celebration normally starts at night, at 7 p.m and goes into the late hours of the night.
Here is the special Google Doodle for the event:
You can see the Doodle today on Google Nederland.
Forum discussion at Google Blogoscoped Forums.