Here's one where a careless wizard gets snatched away by something he summoned and now things from his abode are getting out and causing trouble.
In Ptolus, summoned extraplanar creatures like demons and devils, cannot return to their home plane since the world in which Ptolus is located happens to be a prison plane. The adventure wasn't written for Ptolus of course, so the DM needs to figure out where the wizard went and if he's still alive. Maybe he was taken to the Dark Reliquary to be tortured and killed.
Meanwhile, the authorities are looking to hire some delvers to go in and put a stop to the troubles that are coming out. A successful mission will earn the party 2,000 gold pieces.
There are other interested parties that want something from the place as well. Three different magic users each try to arrange secret meetings with the party (somehow they each learned that the party got the job) to discuss what they each want.
The first is interested in acquiring anything in the way of magic that will help see or hear over distances. He offers 1,000 gold just for searching and bringing these things out. Negotiation of the price is a separate discussion.
The second wants the wizards flying carpet and offers 2,000 gold for it. She can be negotiated upward, but not too much higher.
The third is a bit of a jerk. He wants to know when the place is safe to move into and wants everything on the property to remain. His offer begins at 5,000 gold and can go as high as 7,000 gold. If rebuffed he will attack and run off.
The wizard's estate is larger than just a tower, though it does have one. His garden and abode are well defended by all sorts of traps and creatures. That includes some zombie gardeners which the city would be quite upset about if they knew.
Placement of the estate could be anywhere, but it feels like it would work best in Midtown, maybe along Vanish Row near the river.
If the party thinks this would make a good place to make into a home and headquarters they'll need to go through all sorts of official hurdles and spend some serious money to make that a legal reality. The jerk wizard would also challenge their efforts to gain the deed, assuming he's still alive.
Plenty of fun to be had with this scenario.
