How much thought have you given to game elements/structures that are part of the campaign's flow and evolution, independent of the individual adventures' structures? I'm reading Erin Morgenstern's new book _The Starless Sea_, which is a fairy-tale-like novel told through nested stories like the 1001 Arabian Nights, and exploring their structures, some of which are meta-fictionally self-reflective/-reflexive, a la Borges or Robert Coover. It's a bit like a mega-dungeon of a book, really.
I'm thinking of structures that drive campaigns over the medium- to long haul, like:
- active foreshadowing through backgound/history/sage advice, spies/spying, divination and research spells, prophecies and divine/infernal guidance, etc.
- hidden foreshadowing through returning to earlier locations/NPCs/items/prophecies/etc. that have a newly-realized meaning or significance in retrospect after learning D after A, B, and C ("we should never have sold that wand at 3rd level so we could pay our training costs---it's the X"; "whoa!: we need to head back to that well in level 6 and open that unopenable door with this key now"; etc.); this works best, of course, when specific items, content, histories, etc. have layers of meaning/mystery to them
- assembling pieces and parts of multi-part magic items (Rod of Seven Parts, Eye and Hand of Vecna, etc.), maps, information/lore, paintings, etc.; Anthony's Black Journal falls into this category, I think, in addition to being an awesome prop
- red herrings, false trails/false alarms, and misinterpretations: player agency means that they'll get distracted by the fake ghost's tricks rather than unmasking the fake ghost, sometimes; this is possible through their own misinterpretations, as well as through being distracted by false trails/fake news clues intentionally created by NPCs---I'm thinking of Urgaan of Angarngi's map from Leiber's "Jewels in the Forest" here, or Eclavdra's false trail luring the classic GDQ players to assault Lolth as the root of all of their woes.
- independent actors with their own agendas that drive their goals, priorities, relationships, etc.---this is the whole "putting it all in motion" to create verisimilitude
What other kinds of tools like these do you use to structure long-term campaign play?