Before you set out to Undvik you can go to New Port Inn to get extra info on how to reach the island. Now once you are ready get on a boat in the harbor and off you go. If you ever road a boat near the island then you may have the option to reach the island through fast travel while steering your boat, just use the anchor icon if it's there and done. Keep in mind that this quest is long especially if you wish to save every survivor, so feel free to take your time to explore the island while at it, as you'll have to search most of it anyway. If you made shore on the northern part of the island then move southeast to the nearest village on the island - Marlin Coast, along the way you may find some graves and shields with the An Craite clan symbols. Once there you will have your first fast travel point unlocked. Now follow the main path that goes slightly to the south and then west, if you are uncertain which way then use your minimap it will lead you toward your quest marker. Eventually you will reach a point where a cutscene will play in which the Ice giant is feeding raw meat to the sirens and someone inside the ship that is nearby. After the cutscene you will have the option to explore the ship or move on.
Once you get close to the ship you will hear singing, so climb your way inside through the opening. Inside you will meet an old man named Octo, talk to him, depending on your choices and how you converse you can discover his true identity. Apparently he is a bit mad as he says he and the Sirens are preparing the boat for the giant before his battle with the gods and the meat the giant feeds them is from all the humans it has slain. After asking about Hjalmar and obtaining directions to the camp he will ask for some Twine and Nails, you may already have twine, but the nails you will have to find (regular ones don't work the ones he wants are quest items). Once you are finished there get out and follow your minimap to your new quest marker. The camp is more like a morgue, use your witcher senses to examine the place. Now you will have two tracks to follow, footsteps and tracks left by a boat being pulled.
Following the footsteps you will find a dead Nekker and some arrows along the way, later some more dead nekkers and eventually the trail will take you to the Abandoned Village. Now keep following the trail north and they will take you to a body, and to the left of it you can find the Hornwall horn so feel free to take it as your own now. Nearby you will also find more footprints of the archer and some Trolls, that will lead you into a cave. Inside you will encounter Ice Trolls, keep navigating through the cave and Geralt will make a remark about something getting cooked. Eventually you will hear some trolls talking about soup, once you get close enough Geralt will start conversing with the trolls. They are cooking the archer who will yell to you for help, you can either kill the trolls or decide to play a guess game with the trolls, if Geralt wins the man goes free, if he loses both are cooked. First it's the trolls turn, the answer is easy it's "troll" next it's Geralt's turn, he makes a riddle up on his own, "I'm as light as a feather, but even a troll can't hold me for long." which the trolls guess incorrectly to be "pee" (the correct answer is most likely "breath"). The man you saved either way is Folan, he may ask you about Cerys if you already completed Possession you can tell him how she is doing if not then Geralt says he doesn't know. Regardless you need to ask him about Hjalmar and rest of the company. After the conversation he will join your party and help you with his bow. Now go back to the camp to follow the other trail
Note: By saving him he also becomes a potential ally during The Battle of Kaer Morhen.
The boat trail
Following the drag trail you will eventually find the boat and a dead body and soon after Urskar. There you will find footsteps that will lead you to a cave. While traversing you, will find a body if Folan is with you he will identify it as "Thorsten." Now climb the wall near him and keep going along your new path. Soon you will find another body "Arvid an Tordarroch," now climb the wall again. Eventually you will find a chamber containing a tree and Harpies guarding it, so you can kill them. Use the ladder at the opposite end of the chamber to climb up or you can go to the lower level to loot some chests first. Soon you will reach a corridor that will take you to the exit and you will reach Clan Tordarroch Forge.
Note: This is the place you need to reach to find the tools required for Master Armorers so feel free to do it now.
Enter the house and a cutscene will play where you find a "butcher shop," Folan will tell you none of the bodies belongs to Hjalmar, but you will witness someone making a run for it, after it's over fight the undead and use the other exit. Follow the footsteps and eventually they will split, one will be human, the other the giants, although both take you to the same place follow the human for your quest markers to update. Soon you will reach Dorve Ruins and with it Hjalmar. Kill off the sirens and a conversation will begin, If Folan is with you he will join it too. After the conversation it's time to head out to confront the giant.
Note: If you explore the town you can find the nails the Stranger required, however if you wish to deliver them you should do it now. You can also find a skeleton that has a map and key as part of Ruins, Hidden Treasure, You Know... so you can do that too. Hjalmar won't mind he will just say he will wait for you by the cave if you move too far away, same goes for Folan.
Now go back to the Stranger and give him what he requested. After that just use fast travel to get back to Dorve.
The Giant and the Loon
Once you reach the lair a cutscene will play where Geralt and Hjalmar clear a path. After that go inside and reach your main goal. The giant is sleeping, but you will also find Vigi the Loon in a cage, Hjalmar will tell you to leave him there, you can agree or not, regardless you can free him anyway. You need to avoid walking on snow to get the key without waking the giant. If you fail Vigi will die, if you succeed he will join the fight, but as his name implies instantly wake up the giant by kicking him.
Note: If he survives he will also be able to join you for The Battle of Kaer Morhen.
Regardless it's time to fight the giant. So prepare yourself with Ogroid oil and whatever else you need. After the giant is down by about 33% a cutscene will play where it knocks Geralt away and picks up an anchor as a weapon. After the giant is dead the quest ends. Now another conversation will take place, Hjalmar will make sure everyone hears about Geralts victory over the giant, you can choose to accept or tell him to take the glory regardless you will now have the choice to stay or go with him/them. If you stay he/they will be waiting at the harbor, while you get to loot all containers and the giants remains. You can later meet Hjalmar in Marlin Coast, if you talk to him he will talk about returning to Ard Skellig and ask about his sister, if Possession was not yet completed he will ask Geralt if he intends to go to her, if you answer yes he will be glad, but regardless it's your choice if you help her or not.
- It is a truth universally acknowledged that children only prove more troublesome as they mature. In Crach's case, any troubles his offspring had caused him only doubled after King Bran's death, when both his son and daughter joined the ranks of the claimants of Skellige's throne. Tradition demanded the next king be a great hero, and Hjalmar, Crach's son, felt he fit the bill perfectly. As anyone versed in fable knows, there is no more fitting way to prove oneself a hero than to kill a giant - and it so happened there was one such beast in desperate need of slaughtering on the nearby isle of Undvik. Thus Hjalmar had organized an expedition and set off to earn his glory. Unfortunately, there'd been no word of him since and the jarl had begun to worry. Like many before and after him, he took this worry to the witcher.
- Geralt set out to find Hjalmar an Craite, but first came across the lad's companion in arms, a man by the name of Folan. Folan told the witcher that Hjalmar's crew had scattered when the giant attacked. As for the fate of Hjalmar himself - that Folan could not tell him.
- Geralt searched every inch of Undvik until he finally came across Hjalmar near the giant's lair. Hjalmar had journeyed there to free Vigi, one of the members of his crew. As he deemed the cause a worthy one, Geralt decided to lend Hjalmar his sword.
- Helping Hjalmar an Craite did not prove easy. Undvik had gone feral after the ice giant drove its inhabitants away, with monsters running amok on the island as though it were some mad mage's experiment or a misguided entrepreneur's attempt at an innovative hunting preserve. Yet in the end the witcher triumphed, not only finding Crach's son, but also helping him kill the giant and avenge the men the beast had murdered. His heroic deed accomplished, Hjalmar could now leap out of the starting blocks in the race for the Skellige crown.
- Ask Crach an Craite about Hjalmar.
- Ask around at the New Port Inn about Undvik and the Ice Giant.
- Sail to the island of Undvik and search for Hjalmar. (100)
- Explore the ruins of Urskar and search for signs of Hjalmar's presence using your Witcher Senses.
- Explore the boat's hull.
- Talk to the stranger.
- Help the stranger drive off the sirens.
- Find Hjalmar's camp.
- Explore the remains of Hjalmar's camp using your Witcher Senses.
- Use your Witcher Senses to follow the tracks of those who fled the camp before the attack.
- Find the man the trolls captured using your Witcher Senses.
- Help the man in the cauldron. (200)
- Follow the boat trail using your Witcher Senses.
- Find those who ventured off toward the tower using your Witcher Senses.
- Find out what happened to Hjalmar's crew.
- Follow the trail of blood using your WItcher Senses.
- Find out what happened to Hjalmar's crew in the caves.
- Cross the lake.
- Find Hjalmar.
- Find a way to the giant's lair.
- Avoid snow - the sound of it crunching under your feet will awake the giant.
- Find the key to Vigi's cage using your Witcher Senses.
- Free Vigi. (200)
- Kill the giant. (100) + (500 completing quest)
- The stranger in the boat hull asks for nails and twine. You can find nails as quest items in the surrounding area and at the village where you meet Hjalmar. If you return to the stranger before the quest is over you can give him the nails and twine (which may come from the shackles found near the boat hull) for 200 and additional dialogue.
- You have an opportunity to do this part of the quest after helping Hjalmar kill the giant, but if you do you will not receive any XP, because the quest completes as soon as the giant dies. To do this, just make sure not to meet him on the beach when given the dialogue option.
- This is one of the more badly directed quests in the game. You can even skip whole sections of the quest simply because there is no marker for them and the markers that do exist are often inaccurate. In addition to that, paths from the various sections of the quest lead all over the island crossing over one another so watching a walkthrough might be helpful. There are three parts of the quest that are easy to miss out on. You need not do any of them but they contain items, allies, and information about the sideplot.
- After the siren cutscene the entrance to the under-construction ship is easy to miss and markers will appear if you continue past it. Go underneath and look around using a light source until you find the place to climb up inside to meet the crazy old jarl and his collection of skulls pals.
- After talking to Octo, be sure to follow the arrows west to the Abandoned Village to rescue Folan from becoming troll stew, as you will find the Hornwall Horn along the way. He will also fight for you at Kaer Morhen if he survives the fight with the giant.
- After you emerge from the cave and go through the giant's larder, the trail of footprints leads down a path that diverges. The giant footprints continue to the right and eventually go up over a cliff where you cannot follow. The man-sized footprints lead to the left and into a ruined village (Dorve Ruins) where you find Hjalmar under attack from Sirens.
- When speaking to 'Jonas the Innkeep' during the "ask around the New Port Inn" portion of the quest, he refers to Tante as 'Rante'.