Ancient. Cult. Good luck with writing the campaign. It can be daunting but also a lot of fun.
I am trying to write an entire world. So far I have started with drawing a map then writing the main races. It's a crazy project.
That's a pretty big undertaking. Have you ever seen the 30 days of worldbuilding Post? It might be helpful in creating your entire world. Each day consists of a short 15 minute exercise but it goes through most everything you'd need to think about when building a world. Might be a helpful resource. Good luck!
What an awesome resource! I hadn't stumbled on that before and thank you! So far I have just been brewing it all in my head, I am loving the feedback that I am getting this way. I promise at some point if I ever get this all together I will definitely share the credit.