“ A casual remark by one of the party about something met on a previous adventure leads to a summons to and grilling by the Mages' Guild (or equivalent), probably resulting in an expedition back to that area to recover the things for study by the Guild. The party's presence will be 'requested' for this expedition.”
“ The city was cursed many years ago. Since then it has not stopped raining. The gutters are inhabited by eels and the doors are on the first floor, coated with pitch. On a bad day, you can see the water level rise above the ground floor windows. Carts have both wheels and bladders filled with air to keep them afloat. And yet everyone is surprisingly dry.”
“ God has been slayed by a mortal man and his head is now worshipped and put on a pedestal. The PCs are hired to steal the head and bring it to a mystic that claims to have the power to revive God.”