Realm travel back to Midgard
With his newfound knowledge, Mimir has a plan on how the duo can reach Jötunheim. Exit out of the hidden library, take the elevator down and realm travel back to Midgard. Head over to the now united dwarven brothers and have them make the key needed to enter Týr's mysterious door.
Access the shop to find a whole host of new recipes to craft, this is thanks to your new ability to travel to Niflheim. The Niflheim armor is up there as the best available in the game but takes a lot of time in Niflheim getting the resources. The armor can be very powerful indeed and even trivilize the final encounter in the game, it's for this reason that it's best to save both Muspelheim and Niflheim for after your journey is over and wish to take on the game's most challenging foe where you will need all the assistance you can get.
Note: If you're on the harder difficulties then by all means feel free to tackle Muspelheim and Niflheim now to get any advantage you can muster. Head over to their respective sections to find out more.
You can however upgrade the Blades of Chaos to Level IV with the Chaos Flame you obtained back in Helheim. The final upgrades to the Leviathan Axe and the Blades of Chaos cannot be obtained until after the journey is over and you've put some time into the optional realms. Check out the Skills screen and purchase all the new skills for the Blades of Chaos. Finally, before you leave, the brothers have one final favor for you to tackle, Hail to the King, and it's a good idea to do this now as the reward is very useful.
Hail to the King
Use the Mystic Gateway to travel to the Svartalfheim Realm Tower and light the brazier while you're here. You should also be strong enough to take down the Traveller and after, ride the elevator down to the boat. Head north and then west through the tunnel, taking a right to arrive at King's Hollow and dock the boat.
Head forward and activate the Mystic Gateway before using the entry stone on the nearby pedestal. Follow the path, burning the brambles in the process and taking the chain down. Continue along this path, reading the Lore Marker and finding Sindri at a shop. Speak to him to learn more about the situation and then purchase anything from him should you need it. As you walk forward, you'll spot the final dragon that needs freeing in the distance.
Follow the path and defeat the two Hel-Walkers that spawn, throwing the axe at the Scorn Pole after. Follow this to a coffin that, when opened, springs a nasty ambush. Take the Hel-Walkers out and then look over to the wall from where the coffin is to spot the first Raven.
Head back and take the other path down, defeating any Hel-Walkers on the way and looking to the left to find the next Mystic Gateway. Continue down the path, taking out another Hel-Walker group and at the bottom throw the axe at the Scorn Pole to reach the doors leading into the Stronghold.
Collect keys to enter Stronghold
The door requires three keystones to be placed in the pedestal in order to open it up with the first in front of you. Pick it up, place it in the pedestal and then take off to the south in search of the next. Follow the path past the Scorn Pole, beyond the brambles and past two Wulvers to reach some ruins where a Soul Devourer rests.
You should be used to how these battles unfold by now, wait for the core to become exposed and toss the axe at it to deal major damage along with hurling the clusters that fall off back at it. The Soul Devourer has no new attacks so you can expect to dodge the beam attack only if you keep at somewhat close to it. Upon it's death, loot the spoils and burn away the brambles to find a coffin.
Follow the path up the stairs (and ignoring the wind trap for now) and shimmy across the wall to the other side. Defeat the Wolves at the end and look across to the southeast to spot a Light Crystal hanging, toss the axe at the runic disc to drop it into the stream below. Drop down yourself and pick up the Light Crystal, carrying it with you along the path and through the gate.
Defeat the Wolves waiting to pounce and then resume carrying the Light Crystal down the north path, placing it in the pedestal at the end once the Wulver and Wolves are defeated. Shoot the Light Crystal to errect a bridge overhead and then follow the path back to the south and through the ruins to find the wind trap you ignored earlier.
Grab the Winds of Hel and run up the stairs, across the newly errected bridge and deposit it in the next wind trap. Do this one more time, depositing the energy in the door at the end to find two sacks of Hacksilver. Climb the ledge and look to the left to find the second Konùnsgard Stronghold Entry Stone. Kick the shortcut chain down and head back down to the door to insert the stone. This opens portals in front of the door where Hel-Walkers will come pouring out of. The Hel-Viken is particularly nasty here, as it has more armor than the regular ones, thankfully all your Runics should be available as well as a Summon, this should take them down relatively hassle free.
The north path beckons, start heading that way and look to the waterfall on your west when you reach it. Toss the axe at the wooden boards to lower the water level and gain access to a couple of Hel-Walkers and a coffin. Continue along the path and a Fierce Ogre will block your path as you reach the clearing, defeat the brute and the Hel-Shadow Scouts up high. With the enemies defeated, head along to the south, climb the wall and leap across the gaps to a coffin.
Drop down and kick the chain down before climbing the small ledge to the south. Look up here to spot the next Raven and then pick up the sack of Hacksilver at the end. Retrace your steps to where you kicked the chain down and continue along the northeast path where the dragon, Reginn, is bound.
The Fire of Reginn
Shift your attention to freeing the dragon while you're in this area, after all you'll need to search the area for the keystone anyway. Wait for the dragon to blow a blast of energy and then dash down the hill where two Shadows and the first Dragon Statue is. Defeat the enemies and break it to cause more enemies to spawn. Take the time to go about clearing the area, you'll be up against all manner of Tatzeulwurms so make use of your area of effect Runics.
With the area clear of hostiles, open the southeast gate for a shortcut and then proceed down the north path to reach a Nornir door. Grab a Shatter Crystal from the world tree stump nearby and toss it on the left wall in between the two bells. Shoot this Shatter Crystal and then shoot the Shatter Crystal on the right to activate all Rune bells and open the door.
Head through the door to find a Cursed Tatzelwurm with an explosive jar above its head. Knock the jar down onto the poor Tatzelwurm and defeat the other two that spawn shortly after. Go through the gate and knock the bridge down, checking below the bridge as you cross it to spot the third Raven. As you round the corner, have Atreus read the Lore Marker and then leap the gap after.
A tough encounter awaits you in the next clearing, two Tatzelwurms are assisted by a high level Dark Elf Lord. Not only that, Reginn will rain down electrical bursts on the area dealing damage to both you and the enemy. Try to take advantage of this by watching for static circles around you and baiting the Dark Elf Lord into it, making use of your own Runics to help take it down. Once defeated, destroy the second Dragon Statue and pick up the third and final Konùnsgard Stronghold Entry Stone.
Take the zipline back down and follow the east path to spot a Reaver with a shield. unfortunately for that Reaver, an explosive jar hangs above him, knock it down and destroy the final Dragon Statue in the corner. Return up the southeast hill and have Atreus destroy the anchor to free Reginn and obtain the Scale of the Mighty Epic Enchantment, another Dragon Tear and a Trophy if this is your last dragon to free.
Free all of the Dragons
Look behind this anchor to spot another Raven waiting to meet your axe. With the final keystone in hand, make your way back to the large doors and insert it into the pedestal. The doors finally open, granting you passage into the Stronghold.
Explore the Stronghold
Head forward and take a right, another Jötnar Shrine is hidden here along with a sack of Hacksilver. Take a left in this room and climb the ledge to find a coffin containing the Mark of the Element Epic Enchantment and the final Raven perched above it. Cross the previous corridor to find another sack of Hacksilver followed by another set of doors to head through.
A Traveller has already precast a Runic attack, hold out your shield to block the attack and then begin striking him with the Leviathan Axe. Hel-Walkers join the battle as his health drops but continue to focus on the Traveller before switching to the Blades of Chaos to take out the rest of the enemies.
Don't forget to loot the spoils on the ground after, especially those belonging to the Traveller and then follow the bloodstains to the throne, searching behind it to discover the fate of the Dwarven King. You'll obtain the ingredients you were looking for, Dragon's Fury, Screams of the Innocent and Ultimate Sacrifice. There's also a Lore Marker on the ground detailing the price the late Dwarven King paid.
Take the stairs up and at the fork, take a right to find a Legendary Chest containing the Prometheus Flame Heavy Runic Attack for the Blades.
Note: This is arguably the best Heavy Runic Attack for the Blades of Chaos. Not only does it deal massive damage but it's fantastic for crowd control too, be sure to equip and upgrade it right away.
Take the other path now and follow the path until yet another fork is presented. Head through to the east to find a Nornir Chest with an active wind trap to the side of it. Turn around to face the wall to find two more wind traps on the left and right walls. Grab the Winds of Hel and deposit it in the right trap first, taking it out once the rune is displayed on the bell. Quickly deposit this in the left wind trap to begin having the two remaining runes cycle on it. Use the axe to strike both runes on the left before hitting the final one on the right to unlock the chest.
Head back to the west and follow the path to the south to find a Realm Tear on your right. You'll be up against three high level Hel-Vikens, this is the perfect time to test out your new Runic and combined with the Talisman of Unbound Potential will make quick work of the trio. Close the tear after to obtain Pure Essence of the Realms, Dust of Realms, Perfect Eye of the Realm and 5000 Hacksilver. Take the nearby chain back down to the Mystic Gateway and use it to travel back to Brok's shop.
Hand the ingredients over to the brothers to complete their final Favor and receive the Fire of Ares Heavy Runic Attack for the Blades, the recipes for their powerful armor and a Trophy.
Like Oil and Water
Complete all of Brok and Sindri's Favors
Take a look at the shop now and provided you have enough Hacksilver on you, you can craft one of the two sets from the ingredients you found. Sindri's set is the better of the two to go for, it's Perks are a lot more useful, especially if you use a lot of Runics. Next up, work on upgrading this armor set as high as possible, this should raise Kratos' level to 7.
With this side errand complete, resume your attention to finding Týr's mysterious door. Head out the shop, take the east stairs down to the bottom and follow the path to the north to locate the decorated door.
Explore Týr's hidden chamber
Take the stairs up and shoot the Light Crystal to errect a bridge, crossing it to find yourself back in the Realm Travel room, this time however you'll find yourself below the world tree. Go to the west of this room to spot the upside down Jötunheim door and go through the now open door to the left and across another light bridge. Make your way past the tapestries and into the first room on your right.
Walk forward to find yourself on the other side of the upside down door and approach it, Kratos has an idea. As he goes to flip the room, you'll discover that two chains are holding it in place, you'll need to break these if you're to flip the room. Have Atreus read the runes on the left statue to let him write the answer in the sand bowl causing a switch to appear. Push the switch to activate the lift and descend.
Break the chains
Once you arrive at the bottom, look behind you to find the next Jötnar Shrine, just one more to find. Approach the edge of the room to the east, Kratos makes note of Týr's statue army and, of more importance, that you'll need to make your way around to the chains.
Turn around once again and open the north gate, more death traps await you, these ones a little more intimidating than the last ones you came up against. Toss the axe at the runic gear in the center of the first blade wheel and wait for the second to become visible before recalling. Now throw the axe at the second blade wheel and wait for the first wheel to become aligned with the second before recalling the axe. You'll now be able to spot the runic disc on the third wheel, toss the axe at it and again wait for the other wheels to come around and align themselves. You'll need to repeat this tactic for one more wheel (there's no need to do this for all of the wheels) to create an opening through to the other side.
You'll immediately spot the wind trap as you enter this next chamber and to the right of it, another trap corridor with an inactive wind trap on it. Grab the Winds of Hel and deposit it in the wind trap on the right wall of the blade corridor. This rotates the wheel in front of you, wait until the blade is horizontal and deposit the winds in the wheel ahead. This will cause it to move into the wall and allow you to pass through. Grab the energy from the next wheel and return to the previous chamber to deposit it in either of the inactive traps. Now grab a different Winds of Hel and deposit it on the other inactive trap to open the door and find a Legendary Chest inside containing the Hyperion Grapple Heavy Runic Attack for the Blades of Chaos.
Note: Hyperion Grapple is useful if you want to close the gap between yourself and the enemy. Upgrading it will add a concussive blast when you reach the enemy. A useful Runic but there's better alternatives.
With the chest opened, grab the energy from one of the wind traps and deposit it back on the first blade wheel to reactivate it and then grab the other one from the door to deposit it back in the second blade wheel. Wait for the wheel to rise to the top and grab the energy again, depositing it in the third wheel when the wind trap becomes available. Wait for the wheels to move apart and make your way through to the next chamber.
You'll find a Lore Marker on the wall and a Legendary Chest in an alcove, open it to obtain a Niflheim Cipher Piece if you haven't already completed the language disc, otherwise you'll obtain a random Enchantment. Head over to the chain and interact with it to break it, triggering a trap in the process. A podium will rise from the center of the chamber with two constant bursts of flame. To make matters worse, realm tears open up as Draugrs assault you, watch your surroundings and take the enemies out using Runics. Eventually, a Fierce Ogre will join the battle, turn your attention to it to stun and mount it, using the brute against the rest of the enemies.
Once the enemies are defeated, the flames will deactivate allowing you time to loot all the spoils on the ground. Begin to make your way back to the previous corridor, another podium will rise in the next chamber along with more enemies attacking. This time the flames will rotate around the room so you'll need to be on the move constantly. Like the previous room, make use of area of effect Runics and Summons to take the enemies down and stop the flames. Make your way back through the blade corridor here and open the door to the south.
This time you'll have to deal with spiked blocks moving up and down, wait for the first block to rise and hit the runic disc to freeze it in place. Wait for the second block to lower and recall the axe to have the two blocks moving alternatively. Wait for the second block to rise and throw the axe at it to freeze it in place. You can now head forward and wait under the second block for the third to rise, giving you an opportunity to dash through to the other side.
Open the coffin in the next chamber to obtain the Bracers of the World Serpent and take a Shatter Crystal from the nearby world tree stump. When the first spiked block rises in the next corridor, throw the Shatter Crystal on the ground and trigger it to destroy the ground, causing the spiked block to go low enough for you to walk on to. Wait for the next block to drop and continue your way over to the other side from on top of these blocks.
Another Lore Marker and Legendary Chest containing a Niflheim Cipher Piece awaits in the next chamber. Head over to the chain and have Kratos break this, your goal here is done however you have some company. Not only will you have to deal with the flame jets but a Hel-Traveller and a Traveller Champion, this is a fearsome duo. You'll want to use everything at your disposal, the Prometheus Flame Heavy Runic especially is very useful here. If you find yourself low on health, make use of Spartan Rage, now is as good a time as any to use it.
This difficult battle doesn't end there as some Hel-Walkers will begin marching towards you. Take them out and make your way back to the previous chamber. One last podium rises out of the ground shooting flames in four directions. Another wave of Hel-Walkers accompanied by two deadly Hel-Vikens will attack. Hopefully your Runics are available here, you'll need to make use of them if your Spartan Rage was used in the previous battle.
With all of the enemies cleared out, make your way back to the lift and take it back up. Head forward once more and interact with the Jötunheim door, Kratos uses his gargantuan strength to flip the Realm Travel room. Climb the wall to the left and open the large doors once you reach the top. Dash over to the object at the back and collect it, you now have the tools needed to reach the Realm between Realms.