In monotheistic cultures the holidays are fairly well regimented. Festivals and other events and rituals happen on a well understood cadence.
But what of a world filled with magic, where a multitude of gods are real? What does a holy day look like? On whose schedule does it fall? Is it recognized by the local authorities or just individuals? And who exactly celebrates it?
A simple exercise: Count up all of the deities in the various pantheons of a world. Each of them have holy days, festivals, and solemn rituals devoted to them. Some of these will overlap with each other. In any large city with a diverse enough population, you can easily find some group engaged in some holy day or festival for any given god, demigod, and even a few elementals and fiends.
These events are so common, in fact, that it comes as no surprise when your favorite spice merchant has closed shop on a random day with a cryptic sign about the “blood moon” on their shop window. Or when the local constabulary seem a bit jumpy because this week that one trickster god’s worshippers are pulling well-orchestrated and dangerous pranks throughout the city. Or when you’re awakened some random summer morning before the cock crows by a loud procession of drummers who are both literally and figuratively beating the world to life on behalf of their god.
Just as the old saying goes… it’s five o’clock somewhere… well, every day is a holy day… somewhere. And it’s very likely that somewhere is exactly where you are.