This Trophy / Achievement is unlocked by discovering all Dwarven Shelters in Svartalfheim, part of the Dawn of Ragnarök DLC.

There are only four shelters to be found: the Jordber Shelter, Grenhellir Shelter, Jordegyr Shelter, and Hodda Shelter. You can see our page on the Seeking Shelter quest for a full guide on how and where to find them.