<Insert 4 panel meme with last panel captioned "you prepare?">
Players doc completed and handed over to the players, I know what the first adventuring site will be, know what the big treasure will be, what the final room looks like, know which Dyson Logos map I'm using (the wizard tower from Monster Overhaul) and a general idea of what's in the tower, although exact details are still TBD.
Basically, it's a ruined tower of a dead wizard in a new sandbox campaign set in a land ruined by a wizard war. This particular tower is mostly cut off from reality, although the means to access it has just become available again and an NPC traveling with the party will see the tower on an "empty" hill unless it's viewed from between two trees. (The previous trees around the hill were all destroyed, although two new saplings have now grown close enough for the door to work.)
Inside, the former occupant is long dead, clutching a bronze wand from a previous age (meaning it uses a Dungeon Crawl Classics version of a spell, not the Shadowdark one) and his servants and protectors -- the ones that weren't destroyed by his opponents -- are only semi-functional.
So I still need to figure out what sort of animated objects, etc., are stumbling around in the tower and if there are any half-functioning traps the party needs to get past.
This is just meant to give the PCs an introduction to the area, establish that the wizard ruins are there for the plundering and hint that there's a currently unknown reason all the wizards came there to begin with. (The relic of the bygone era, along with a strange mural in the room where the former occupant's corpse now lies, depicting a "sunrise" -- a bronze semi-circle -- rising over the northern mountains, rather than where it should be.)
The NPC that sees the tower is a historian, arriving in the region alongside the PCs in the obligatory convoy. Once everyone arrives at the sandbox's home base and the PCs are about to start shopping and settling in, riders will swoop in, grab the historian and be off before the PCs (who are on foot) will be able to respond, further suggesting that the secret history of this region should be of interest to everyone.