"At midnight, especially on Walpurgisnacht, the Devil holds picnics in the graveyard"

 

 Walpurgisnacht is a spring festival which takes place every year around the 1st of May in Northern and Central Europe.  It is similar to the Celtic celebration of Beltane, or May Day.  Translated from German, it means 'Walpurgis Night', and is named for St. Walpurga; although traditionally it celebrates the end of winter and the coming of Spring, it has a much darker side too.  In Germany, where this story is set, it was believed that dark forces were able to gather together in order to take advantage of the final day of winter.  In particular, witches were said to assemble on the Brocken - the highest peak of the Harz mountain range - to hold their Sabbat.  Their revelry would conjure up the Devil, and together they would commit terrible acts.  People celebrate the festival with the lighting of bonfires, especially in the smaller, rural towns near the Harz mountains., and often dress up as witches.