“ 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 village sits on the edge of the deep fjord, often engulfed in mist or rain. Its people are fishermen, who work even through the sea-ravaging winter. And they pray to the gods of the deep.
At the beginning of every winter they hold a summoning ceremony. Three boats are taken out into the fjord, a hornsman on each. The mournful horns are blown in the language of the whales, the gods of the deep. The whales sometimes appear in answer to these calls, and it is taken as a good omen when they do.
To a party of PCs wandering the misty hills and valleys nearby however, the doleful whalesong of the horns can be disturbing and misinterpreted...”