The reference page. Series chronology from year minus thirty-one through Akron. Faction tree showing the Vatican, the Council, and the Ninth Circle. Character relationship chart. Open threads.
The reference sheet I wished I'd had on my desk while drafting Raven's Rise — chronological reading order, the geography of Raven's Peak and the Council, and a relationship spine for paid members catching up.
The dungeon is the easy part. Building a text adventure game engine taught me the hard half is teaching the machine to listen to what players actually say.
The hard part of a nine-book series is not writing nine books. It is making book seven remember what book two promised. Here is how I keep mine from collapsing.