Ulmerial

Ulmerial, roughly translated from the Sprite language as "Joy of Ul", is a Sprite festival held at the height of summer, specifically on the summer solstice. There is a great dais resembling an enormous magnifying glass on the northwestern edge of the Usulli Wilds that the Sprites use for this festival celebrating their Great Mother Usul the Wild.
At its core, Ulmerial is a feast of absurd proportions. Days beforehand are spent cooking, baking and preparing for the immense amount of food required - much of the preparation being ceremonial in nature. The Sprites rarely share details of their most important religious rituals with outsiders, however it is known that their mother goddess is a great trickster, so it is supposed that the religious preparations of the food are to prevent any untoward effects being placed upon it, as the Sprites are particularly prone to divine intervention due to their close relationship with their goddess.
The festival itself starts at midday on the summer solstice - how this exact moment is ascertained seems to have something to do with the great dais - and effectively is one giant celebration. Thousands of Sprites swarm from the forest to dance and sing and eat their fill. Any mortal who witnesses the event is compelled to join in, and very few are ever seen again. It is from this event that many of the traditional wives tales about the Sprites arise, confusing them with their close relatives from the Feywild - in truth the humans who attend Ulmerial simply travel back to the Sprites pocket plane where time passes differently, and are often returned home hundreds of years later.