On this page of our AC Valhalla Dawn of Ragnarok guide, you can find the locations of Legendary Hoard maps (Legendary Hoard side quest). They are all located in Svartalfheim, and can be obtained only after completing the main storyline of the DLC.
Map of Tove's Tale
Reward: 1500 leather
Location: This map is hidden on a small island just south of Gullnamar.
When you arrive/fly to the island, you will immediately see the only tree in the vicinity. There are many snakes lurking nearby, but they are very easy to defeat with a single accurate blow or a fired arrow. After clearing the area, approach the tree. Your reward is 1500 leather.
Map of Gunnar's Tale
Reward: 10 nickel ingot
Location: You will find this treasure in the southern part of Gullnamar.
Your reward is on a small altar right next to a small waterfall. The area in question is located by the largest tree in the location.
Map of Alvis's Tale
Reward: 1000 iron ore
Location: The treasure is hidden on the walls in the northern part of Svaladal.
To reach the walls, best use the Power of the Raven, it is a quick and safe option. Once your on the wall, travel to the area where the water flows. Your resources are on its right side.
Map of Randvi's Tale
Reward: 250 titanium
Location: The treasure is hidden on a small island in the northern part of Vangrinn.
Getting to this location should not be much of a problem. You can sail or fly to this islet using the Power of the Raven. There are no opponents in the area. All you have to do is approach a small encampment, right next to the water, and you will find 250 titanium there.