Kneel Before Thor!

Map Location:

(After the lake’s water level recedes for the second time) Landsuther Mines, behind the closed gate in the main floor. You’ll only get to explore this area when the favor, Deus Ex Malachite becomes available. To reach it, you’ll have to break the floor to reach the cavern below.

Once there, follow the stream and you’ll see the lift beside a ledge you can climb up on, by the wooden chest. Use the lift and you’ll find the map beside the coffin.

Treasure Location:

The treasure is located at the foot of the broken Thor statue, behind Muspelheim Tower and beside a Jotnar Shrine (Thrym). To reach it for the first time, you have to navigate the new accessible area in the Lookout Tower until you reach a rope that you can use as a zipline to reach the foot of the Thor statue and Muspelheim Tower.

If you already explored the area before, you can head to Muspelheim Tower and use the lift there instead. The treasure mound is located near the edge of the cliff beside the jotnar shrine as shown below.