In the new God of War the Fog Realm of Niflheim is gated behind finding ciphers throughout the world. You’ll need to collect ciphers fragments to access this realm and they’re scattered throughout different parts of the Lake of the Nine and Mountain areas. Accessing this new area allows you to unlock unique gear and go on missions that you will not see in the main story.
There are once again four cipher fragments that you’ll need to track down. One you’ll come across naturally during a story mission that takes you back on your third trip to the Summit.
The other three can be found at the locations below:
Ruins of the Ancient (Lake of the Nine) – This area is located directly north on the map of the Lake of the Nine. Just boat north until you see the ruins. On your left you’ll see a beach with a Soul Devourer stalking around. You can quickly run in and grab the cipher from the special chest or fight the enemy and then gather the item.
Alfheim Tower Beach (Lake of the Nine) – To gather this cipher you’ll want to head just north of Alfheim Tower to the beach right next to it. To snag this cipher you’ll need Atreus shock arrow power. When you land on the beach you’ll see two of the red rocks that can be shot to clear a path through golden rocks. Climb up from here and you’ll see another golden rock to your right. The cipher is behind this rock. While it looks at first like there is no way to clear the rock, there are explosive items behind the rock if you climb above it you can shoot it with shock arrows to proceed.
Lookout Tower Dock (Lake of the Nine) – This cipher is located directly west of Vanaheim Tower on southern side of the Lake. Once you land here you’ll see a spinning contraption which Kratos can turn with the Leviathan Axe. Doing this will lower the spikes that will allow you to progress and snag the cipher. The cipher is located behind two sets of spikes on the beach.
Once you’ve got the cipher you can head back to the World Tree and access Nilfheim. Heading there for the first time you’ll notice that the realm looks much different than the others and has some unique properties. Sindri will be there and he’ll ask you to collect 500 Mist Echos. This will allow him to craft you a key to access a central chamber in the area.