Here is a post letting you know exactly which one is in which location.
Conall's Valley Night (1st instance):
Treasure Chest 1 1577x763
Treasure Chest 2 1674x588
Treasure Chest 3 1709x786
Stolen Vigdis Supplies 1 1787x900
Stolen Vigdis Supplies 2 1672x586
Stolen Vigdis Supplies 3 1704x1169
Blue Mountains (2nd instance):
Stolen Vigdis Supplies 4 307x127
Stolen Vigdis Supplies 5 474x73
Treasure Chest 4 199x465
Fort Storisbjorn (3rd instance):
Dead Adventurer 264x556
Treasure Chest 5 380x293
Treasure Chest 6 574x655
Treasure Chest 7 731x648
Stolen Vigdis Supplies 6 495x461
Stolen Vigdis Supplies 7 458x435
Stolen Vigdis Supplies 8 527x270
Stolen Vigdis Supplies 9 150x423
Greathall of Heimdall (4th instance):
Treasure Chest 8 (1st floor) 155x105
Treasure Chest 9 (3rd floor) 184x174
Stollen Vigdis Supplies 10 (5th floor) 159x212