Short answers, pulled from the story.
May Day traces its origins to at least the Roman Republic era, when the Floralia festival of the goddess Flora ran from the 27th of April to the 3rd of May. Parallel Celtic traditions such as Beltaine in Gaelic culture and Calan Mai in Wales are first attested in 900 AD, centered on bonfires and rituals to protect cattle at the start of summer.
The Maypole is a decorated tree or pole around which people dance and sing as part of May Day festivities. The earliest English records of Maypole celebrations date to the 14th century, and by the 15th century the tradition was well established in southern Britain. Philip Stubbs described 1580s celebrations in which teams of oxen dragged a flower-covered pole home, followed by two or three hundred people.
May Day was abolished and its celebration banned by Puritan parliaments during the Interregnum. It was reinstated with the restoration of Charles II in 1660.
Walpurgis Night is celebrated on May Eve, the night before May Day, and commemorates the official canonization of Saint Walpurga on the 1st of May 870. In Germanic countries it involves bonfires and, in Tyrol during the 19th century, elaborate rituals to drive witches from the village by fumigating houses with juniper and rue incense and running seven times around homes carrying lighted bundles of herbs.
Lei Day is Hawaii's version of May Day, celebrated on the 1st of May as a day to honor island culture and Native Hawaiian traditions. It was invented by poet and newspaper columnist Don Blanding, and the first Lei Day was held on the 1st of May 1927 in Honolulu.
In Edinburgh, the Beltane Fire Festival is held on May Eve and into the early hours of May Day on Calton Hill. At the University of St Andrews, students gather on the beach on May Eve and run into the North Sea at sunrise on May Day, sometimes accompanied by torchlit processions. Edinburgh also maintains the tradition that young women who climb Arthur's Seat and wash their faces in the morning dew will have lifelong beauty.