Not to be confused with Izambri's thread of almost the same name (which is infinitely worse due to the lack of Oxford comma and lack of con-content. Con-tent. Content.)
Let's hear about some conworld holidays! Although I've written about a bunch of Lilitic holidays already, more is always better.
The resettlement of the inner belts was a major event in the history of postlapsarian Thet, and is commemorated each year by the residents of the modern city of Dis and its surrounding demes on nearby islands. In contrast to other anniversaries of events from the period, the Resettlement is a happy occasion and functions as the analogue to the new year in its cultural significance. (The actual start of the calendar year, some two months earlier, is a sombre time, as it is the anniversary of the Shattering itself.) Births, weddings, and agreements are thought to be lucky on this day, and it is a common date for breaking new ground on construction or the renovation of public works.
In more superstitious communities, this luck is said to be brought by a prophet or idol, most commonly Sarthía, Tetragnostica, or Myenga. Although Thessians are not known for their shrewd capitalism, some of these neighbourhoods have taken the notion of luck somewhat literally, and pool their money to purchase a large number of lottery tickets on this day. Symbols associated with the Resettlement include archaic construction tools—cranes, hammers, saws, pulleys, and other simple machines—and acquaintances will often exchange miniature gilded specimens of these instruments, purchased from gift shops, in lieu of other ideas for presents; the act of exchange is sometimes believed to imbue these otherwise useless ornaments as lucky charms. To have "carpainter's wealth" or "a house built with golden nails" are colloquialisms suggesting someone knows many people but has few if any real friends.
Among Hellesans and other Bredezhan peoples, the last feast was Ànvires Dances "Sacred Souls", with agricultural and funerary roots, and celebrated in 13 and 14 brovines. The first day coincides with the celebration of the end of the harvest period, and the second one is the Venerable Deceased Day, celebrated 40 days after the autumn equinox, a day to remember the deceased loved ones, whose spirits work together with berets (genies of houses, homes and families) to protect both the house and the family.
After that feast the next one doesn't have a fixed day because is the tasting of the first (or youngest) wine, which is celebrated throughout the 2nd half of this month (this is, after Ànvires Dances). In towns and cities the custom is to form a small group of people to visit several cellars to taste the first wines; these cellar visits are spiced up with sweet cakes, toasted almonds and hazelnuts, and cheese, as well as music in which becomes, de facto, a kind of popular religious mass. Doing the 'cellar route' is known as ader isont "to go hot" or "to behave hot", and the name of the feast is Enyatzes "large amount of wine".
Feres or fers (roughly, from August 20 to September 18) is the last summer month and I don't know any relevant feast or celebration held during the same. Regarding celebrations it looks like a rather calm and quiet month, perhaps as a subconscious waiting/warning of autumn.
Anyway, the closest thing I've found in the Arcanarchiva™ is romallàs "flashing, lighting-like" (from romall "flash, lightning"), a popular name for this month; another one being tremareu "thundering" (from trem "thunder"). The reason is obvious: that is a stormy month, with the first rains after summer, as well as hailstorms and thunder storms.
According to popular belief such phenomena are caused by anyets, the atmospheric genies that throw lightnings and hailstones. Folktales tell how these anyets throw ice mountains among themselves, and when the mountains of ice clash they're broken into thousands of small pieces of ice, thus producing hailstorms and associated phenomena.
There are no special celebrations or pilgrimages to apaise the anyets, but people believe that laurel trees prevent lightnings to fall nearby, and this is why this tree is so common in rural areas and urban parks. It's also common practice to hang laurel leaves on the outer side of doors.
The rite of cutting the sky with a knife to terminate a growing storm is still common in many countries and shires.