This Trophy / Achievement is unlocked once you complete all of the main story quests in Svartalfheim, part of the Dawn of Ragnarök DLC campaign. Below is a list of all the relevant story missions associated with the trophy:

Restless Dreams Quests

• The Rescue
• Gift to the God

The Relic Quests

• Finding Fritjof
• The Scholar and the Sunstone
• The Vault of the Ancients

Vessel of Souls Quests

• The Warlord’s Daughter
• Cold Embers
• Blazing a Trail
• Malvigr

Into the Fire Quests

• Seeking Shelter
• Hunter and Gatherer
• The Masters
• Forging Bonds
• Warpath
• Pride of the Aesir
• Beyond Fear
• The Reckoning