This will start immediately as soon as you retrieve the piece of the chisel. Head to the sealed door and interact with it to start using the chisel. Move the chisel until you see it glow immensely. This means that it’s on top of a binding point. Press R2 to strike and when done correctly, the chisel will create a crack on the spot it hit. Some seals have at least two binding points while tougher seals may have up to four. You only need to hit a binding point once so once you found one and the crack covers up itself automatically, you don’t need to hit it again.
After opening the door, continue forth to the ruins. There’s another rune-sealed gate here that you can unlock by finding all rune seals in the immediate area. One of the seals is located high above the doorway where you came from as shown below.
Ignore the sap-covered coffin for now and climb up using the metal prods near the chest. Upon reaching the next ledge, kick the chain that leads back to Sindri’s shop but don’t go down yet. Turn around and look for the shatter crystal in side a concave slot to detonate it and make it fall to the ground. Look where it fell and shoot it again to destroy the sap covering the coffin below. However, don’t go down yet.
Find the second seal in the rubble across the ledge. Destroy it then drop down the lower ledge. From there, look up to the right to find the last rune seal peeking above the ice. Destroy it.
From that ledge, drop back to the lower ground and go to the opened gate. Loot the wooden chest and pick up Glacial Catalyst from a troll’s corpse. Next, loot the Solid Svartalfheim Steel from the nearby coffin.
Now climb back up and drop down back to Sindri’s shop. Use this chance to upgrade your Leviathan axe using the Frozen Flame you got earlier. Don’t forget to upgrade your newly unlocked skills as well. Once done, drop down to the dining hall and open the magic-sealed door there to continue.
Follow the corridor and take note of the sap-covered coffin in an alcove to the left. At the end of the hallway by the corner is an empty light crystal base. Follow the path and look up to find a sap-covered light crystal holder. Get past that and destroy the wooden obstructions leading to the shatter crystal sap inside the alcove near the light crystal.
Pick up the shatter crystal and throw it at the sap trapping the light crystal. Now get another shatter crystal and throw it at the coffin. Loot a Solid Svartalfheim Steel from the coffin. Backtrack to the crystal and bring it to the light crystal base. Light it up to reveal a realm tear. Interact with it to get a Dust of Realms. Continue along the main path then exit through the door to the next area.
Go around the corner to the right then boost Atreus up the ledge near the gondola lift cable. Head to the other and destroy the binding that holds the lift to the ledge. This will cause the lift to slide to the other side. Wait until Atreus boards the lift then operate the gear wheel to bring it back to its original position.
Once it does, look up and freeze the gear above the lift for it to stay in place. After that, order Atreus to lower the chain nearby so you can use it. Climb up and vault over to the lift. Recall your axe to make the lift slide back again.
Loot the wooden chest nearby then jump across to the next platform. Turn to the right and kick off the chain from the holder to create a shortcut for you. Once done, head to the sealed door and unseal it to get back to the entrance.
Once you’re back to the dock, you can also unlock the seal leading to the hidden chamber of Odin to the right. Inside, there’s a shrine (Thamur) and a lift leading below to a valkyrie named Gunnr (follow the link to her page for detailed tactics how to defeat her).
The chamber of the valkyrie has a mystic gateway and several chests/coffin that you can loot. You should be more than capable of defeating this valkyrie. Doing so will unlock the corresponding labor and a Legendary Favor for the Valkyries (Prove your Valor). Once ready, you can use the nearby mystic gateway to return to Brok’s shop.
From Brok’s Shop or if you sailed to the lake the way, find the entrance to Tyr’s Vault right beside Tyr’s Temple’s boat dock. Unseal the door and head inside.
Examine Tyr’s shrine with a missing middle panel then the sand bowl. During this cutscene, Modi will appear and attack you. Use your Spartan Rage once prompted to get back up and scare Modi away. This will complete the journey quest and immediately start the next one.