The city turns into one giant block party, with bands, beer stands, street vendors, and an extremely high number of drunk people, mostly wearing some type of orange attire.
For example, please see the foto to the right. Pay no attention to the two party goers on the right, but examine the passed out youth slouched underneath the tree. Not only has he consumed about 7 liters of beer, his hair has been spray-painted orange as a reminder. Party time. Excellent.
... if you ever find yourself in Amsterdam at the end of April, make sure to make the most of these festiviteis. Large orange hats strongly recommended.