You can find Veithurgard near Stone Falls. Once you open the gate to go there, there's one side mission that you will finish: Otr's Stronghold. It's the same as the other dragon missions where you'll destroy 3 sigils and then let loose the dragon. (Be wary of the lightning warning signs when you fight the Helwalkers.)
Afterward, you'll need to get into the big door with the Rune Sigil lock puzzle and follow through the area until you fight the big Ogre. Defeat that and once you open the door, you'll come across a chest. Open that, and the trophy will unlock.