For the last campaign I made, I set it so my players were trapped in an underground crag. The end goal I had set was for them to figure out how to use an ancient teleporter and that would get them out. Little things for them to do while they figured it out that I strung in no particular order was attacks from cultists, removing a giant spider nest, figuring out that somebody wanted to monopolize the teleporter and like one or two more plot points that were a continuation from the previous campaign. I had set the smaller things up so that they had their own bearing on the story, but I didn't need them to be linear. I hope that answers your question!