“ 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.”
“ A modern kingdom still strictly adheres to ancient traditions due to their long forgotten deity getting annoyed at the moral decay, appearing as an AI Singularity and forcefully correcting everything it sees as morally wrong. As such, even though the weapons and technology have improved, the culture hasn't.”