Valborgsmassoafton
"...when witches meet on the Brocken mountain and hold revels with their Gods..."
April 30, 2006
Stockholm, Gamla Stan and Riddarholmen


According to Wikipedia:
Historically the Walpurgisnacht is derived from Pagan spring customs, where the arrival of spring was celebrated with bonfires at night. Viking fertility celebrations took place around April 30 and due to Walburga being declared a saint at that time of year, her name became associated with the celebrations. Walburga 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.