You have to find 3 [object=293700] in Forgotten Cove caves.
There are 5 caves you have to check.
Dark Grotto is south of The Lost Estate near the shore.
Bleak Sepulcher is in the building to the east near the road.
Moldering Foyer is north-east of the The Lost Estate near the shore.
Crumbling Chambers is east of The Lost Estate on the other side of the island.
The Profaned Reliquary is north near the cliff.
/way Stormsong Valley 80.50 57.04 Dank Grotto
/way Stormsong Valley 83.61 53.93 Bleak Sepulcher
/way Stormsong Valley 81.64 50.29 Moldering Foyer
/way Stormsong Valley 82.08 44.74 The Profaned Reliquary
/way Stormsong Valley 86.58 51.98 Crumbling Chambers
Plunder and Provisions video: https://www.youtube.com/watch?v=p8sKUuyYUEw