Historically the Walpurgisnacht is derived from Pagan spring customs. In the Norse tradition, Walpurgisnacht is considered the "Enclosure of the Fallen". It commemorates the time when Odin died to retrieve the knowledge of the runes, and the night is said to be a time of weakness between the living and the dead. Bonfires were built to keep away the dead and chaotic spirits that were said to walk among the living then. This is followed by the return of light and the sun as celebrated during May Day. Due to Walpurga's holy day falling on the same day, her name became associated with the celebrations. Early Christianity had a policy of 'Christianising' pagan festivals so it is no accident that St. Walpurga's day was set to May 1st. Walpurga was honored in the same way that Vikings had celebrated spring and as they spread throughout Europe, the two dates became mixed together and created the Walpurgis Night celebration.
Walpurgis (sw: Valborgsmässoafton or Valborg) is one of the main holidays during the year in Sweden, alongside Christmas and Midsummer holiday. The forms of celebration in Sweden vary in different parts of the country and between different cities. One of the main traditions in Sweden is to light large bonfires, a custom which is most firmly established in Svealand, and which began in Uppland during the 18th century. An older tradition from Southern Sweden was for the younger people to collect greenery and branches from the woods at twilight, which were used to adorn the houses of the village. The expected reward for this task is to be paid in eggs.
The tradition which is most widespread throughout the country is probably singing songs of spring. Most of the songs are from the 19th century and were spread by students' spring festivities. The strongest and most traditional spring festivities are also found in the old university cities, like Uppsala and Lund where both current and graduated students gather at events that take up most of the day from early morning to late night on April 30, or "sista April" ("The last day of April") as it is called in Lund and elsewhere throughout the country. There are also newer student traditions like the carnival parade, The Cortège, which has been held since 1909 by the students at Chalmers in Gothenburg.
Oh- and also it is my 40:th birthday... Whohoo!