Where to find Fog of Fimbulwinter in God of War Ragnarok

This is a runic attack for the Leviathan Ax, which deals crushing Frost damage, but if you don't know where to find it, just keep reading. 

To find this attack you will have to search a chest in Svartalfheim, in the Myrkr Tunnels. To get to it, you will have to use the train to The Forge or use the nearby Mystic Gateway. You will have to go through the hole next to the tracks to go underground, towards the tunnels.

Being in the tunnels you will have to continue forward until you find a camera, through which the natural light from above touches the ground. Here you will see a door is locked. The chest is on the other side of the door, so follow the path to the right until you reach the other side of the door.

The area is covered in red vines that block the chest. So you will have to light the barrel that is on the right to destroy it, from a safe distance or you could burn yourself.

Now you will have to approach the chest and open it to get the attack.