Walpurgis Night is a traditional spring festival on 30 April or 1 May in large parts of Central and Northern Europe. Its celebration is associated with dancing and with bonfires. The current festival is, in most countries that celebrate it, named after Saint Walpurga (ca. 710-777/9). As Walpurga was canonized on 1 May (ca. 870), she became associated with May Day, especially in the Finnish and Swedish calendars. The eve of May day, traditionally celebrated with dancing, came to be known as Walpurgisnacht ("Walpurga's night").
In Germany, Walpurgisnacht, the night from 30 April to 1 May, is the night when witches are reputed to hold a large celebration on the Blocksberg and await the arrival of spring. In some parts of northern coastal regions of Germany, the custom of lighting huge fires is still kept alive to celebrate the coming of May, while most parts of Germany have a derived Christianized custom around Easter called "Easter fires".
In rural parts of southern Germany, it is part of popular youth culture to play pranks such as tampering with neighbours' gardens, hiding possessions, or spraying graffiti on private property. These pranks occasionally result in serious damage to property or bodily injury. In Berlin, traditional leftist May Day riots usually start at Walpurgis Night in the Mauerpark in Prenzlauer Berg. There is a similar tradition in the Schanzenviertel district of Hamburg, though in both cases, the situation has significantly calmed down in the past few years. (From: Wikipedia)