“ 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.”
“ Game Cliche 2.
Upon learning about 'the five ancient jewels' or 'the nine legendary icons' or whatever, you can be quite confident that Saving the World will require you to go out and find every last one of them.”