So I have flyers out and the beginnings of the campaign are finished.
You know what else I've done?
I have this sheet of hex paper with tiny-ass hexes on it, and it isn't filled in any more than that player's starter map on the Olden Domain mailing list site.
I have a basic sketch for one of the dungeons (where the mega-dungeon will be), and a few random encounter tables.
I have a full notebook page of ideas for locations (just lists, mostly), with a rough idea for level spreads and themes, and how they are connected.
But detailed maps?
Not one. And no keys made for these maps that don't exist.
The way I'm doing my sandbox is to not touch anything until somebody says they want to visit. Then I will pour my current ideas into that location, decide what clues that location will have for locating other locations, as they are encountered. This ensures that I don't have to be committed to detailing The Great Pyramid tomorrow because it's the next closest thing on a map I made six months ago if I really want to showcase a brand new idea I had yesterday.
Nothing exists until someone wants to go there!
Wasted creativity, and especially tearing your hair out detailing every damn thing before knowing if it will ever be used, is a referee killer.
What if The Olden Domain absolutely bombs and nobody wants to play in it? (eek!) No time wasted on detailing locations within it.
What if people get excited about that mega-dungeon and don't want to bother with the rest of the wilderness? Or what if they want to explore as much as possible and not fool around with a huge hole in the ground?
I can accommodate their wishes without having any investment in the locations they leave behind. I really hate making a dungeon, leaning on the players to check out this really cool place, and then have them go somewhere else. There is this pull within me to railroad them into it anyway, when the correct thing to do is just let go.
I'm looking at this little sandbox I've planned, and I'm astounded by the enormity of it. To do this properly, there must always be first level-appropriate places to handle the needs of new players (and new/replacement characters!), while also being a succession of locations suitable for whatever level after that. I could sit down and write enough to match the entire output of 1E TSR and still not have a thoroughly detailed setting. At the same time, I don't feel totally comfortable winging an entire dungeon. Sure, "Location #5, Kitchen," I can improvise off of that handily, but I want to know where the kitchen is before anyone walks in the door.
So I'm not even going to start the process yet (OK, I might sketch out a few maps for my own amusement...). I have ideas, but that's how it stays until someone steps through that door.