Evidently today, April 30, is Walpurgis Night, and while I can't say I've celebrated it before or have definite plans to do so today, I must say it sounds rather cool. Here's what Encyclopaedia Brittanica says on it (and it must be true since it isn't Wikipedia):
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Walpurgis Night, a traditional holiday celebrated on April 30 in northern Europe and Scandinavia. In Sweden, typical holiday activities include the singing of traditional spring folk songs and the lighting of bonfires. Celebrations in Finland include a carnival and the drinking of alcoholic beverages, particularly sima, a type of mead. In Germany, the holiday is celebrated by dressing in costumes, playing pranks on people, and creating loud noises meant to keep evil at bay. Many people also hang blessed sprigs of foliage from houses and barns to ward off evil spirits, or they leave pieces of bread spread with butter and honey, called ankenschnitt, as offerings for phantom hounds.
[Molly's interjection: Phantom hounds! How awesome is that? Why don't any of our usual holidays involve phantom hounds?]

The origins of the holiday date back to pagan celebrations of fertility rights [sic - surely "rites"?] and the coming of spring. After the Norse were Christianized, the pagan celebration became combined with the legend of St. Walburga, an English-born nun who lived at Heidenheim monastery in Germany and later became the abbess there. Walburga was believed to have cured the illnesses of many local residents. After her death she was canonized as a saint on May 1. Although it is likely that the date of her canonization is purely coincidental to the date of the pagan celebrations of spring, people were able to celebrate both events under church law without fear of reprisal.
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Other sites give the same basic information; namely, that it was yet another pagan celebration that got turned into a Christian and sometimes specifically anti-pagan holiday. There are reports that in German folklore, Walpurgis Night was when witches met atop a certain mountain, so in a way it's a celebration for witches; but nowadays it sometimes involves symbolically chasing away the witches till next year. Very similar to some interpretations of Halloween/Samhain, that way.

In any case, it sounds like a fun way to start off Beltane/May Day/Spring Day. May you all be the May Queen or Green Man of your personal household this weekend. I did bring in some fresh sprigs of sweet woodruff and orange-mint, so perhaps I'm celebrating in my small way too!