If you are to meet Crach an Craite then he should be very close if you decide to talk to him right after you reach Skellige with everyone. So even if you wish to do something else first you should still talk to him right away.
Now go see Mousesack he will be talking to Madman Lugos who will once again live up to his moniker but this time it will be his last as you will be forced to kill him. Once he and his men are dead you will have to run along with Mousesack, when you are far away he will talk to Geralt and you can ask about the Sunstone. He will not know where it is but will direct you to Eyvind and pearl divers, however he will suggest you bring a Sorceresses with you. See whoever you like, however if you go see Eyvind then don't mention Mousesack or he will refuse to tell you anything.
The Ancient Crypt
Regardless from who you got the location it's time to go see Yennefer, during the conversation Ciri will decide to visit Avallac'hs lab which will start the Child of the Elder Blood quest and add it as a new objective for Battle Preparations, Philippa however will decide to help Geralt with the Sunstone. If you already have the Ancient Crypt marked on your map you can just fast travel there. Philippa will be waiting by the entrance and will open the entrance, so proceed with the search. Soon you will encounter a Siren and Drowners, after taking care of them you can use the Igni Place of power nearby.
Now you will find some ruined staircase however Philippa will fix it allowing you do move forward. The path will split here, if you go left you will encounter a Venomous arachas and a Hidden Treasure, with spikes coming out of the floor. You can use Witcher Senses to see where the spikes are not present to pass of you can use Quen to make it more easy, once you are on the other side pull the lever to turn them off, then go back to Philippa when you are done.
The right path will take you to a Golem, after it's dead and you move a bit forward Philippa will talk to Geralt about Yennefer and Ciri. After that you will reach a room where you will have to turn mirrors in the correct direction. Best way to do this is by starting with the mirror in which direction the central crystal is pointing it's light at, then making it reflect the beam to the mirror on it's right and proceed from there, once the beam goes in the direction of where Philippa is standing the Sunstone will appear. Philippa will now converse with Geralt and try to convince him to leave with Yennefer after all this is over, However if you broke up or you are romancing Triss, Geralt will point it out and Philippa will ask to give Yennefer friendly advice instead. After which she gives Geralt the Sunstone and the quest ends. However, you still need to get out so use the new path that has been opened to climb out of the ruins.
- Geralt knew he could only defeat Eredin with the help of mages and on his own terms. Since the King of the Wild Hunt was traveling on the Naglfar, the spectral vessel known from Skellige legend, somewhere between worlds, our heroes had to summon him back and somehow cut off his escape route. Such a feat could only be performed by a group of mages acting in concert and aided by a legendary elven artifact - the Sunstone.
- The emperor's flagship was anchored in Skellige's waters when Geralt arrived. His Imperial Majesty would preside over the battle in person - but more important to Geralt was the prisoner he held on his ship, the Nilfgaardian sorceress Fringilla Vigo, whose aid could turn the tide of Ciri's defense. Geralt thus asked the Emhyr to lend him his captive sorceress. Though Fringilla was a suspected traitor, Emhyr agreed.
- Geralt overcame countless obstacles and found the Sunstone - a feat which, to give credit where it's due, would have been impossible without the help of Philippa Eilhart. Everyone knew what this meant: the preparations for the great battle against the Wild Hunt had come to an end, and what would follow their activation of the Sunstone would determine the fate of the world.
- If either of the an Craite siblings is ruler of Skellige:
- Or if Svanrige is king:
- The next two objectives are mutually exclusive:
- Talk to the bard known as Eyvind.
- Find and talk to the pearl diver.
- Talk to Yennefer. (Starts Child of the Elder Blood )
- Meet Philippa in the elven ruins.
- Explore the elven ruins with Philippa Eilhart.
- Exterminate the monsters.
- Explore the elven ruins with Philippa Eilhart.
- Set up the mirror system properly.
- Examine the Sunstone.
- There is an Igni place of power and a hidden treasure in the ancient crypt.
- If you plan on completing Gwent: Skellige Style and Collect 'Em All, you must win against Madman Lugos before starting this quest since you will have to kill him.
- This only appears to happen if you sided with one of the an Craite children.
- The quest will progress once you successfully learn the location of the cave from either the bard or the pearl divers. However, even if you succeed with your first attempt (e.g. convince the bard) you can still visit the other location (e.g. pearl divers) and complete the interactions there prior to going to Yennefer. Putting a marker on the map prior to visiting either location is a good way to remember where to go.
- It is advised to explore the caves, as there are a number of good loot chests in nooks and crannies.
- The right answer to convince Eyvind, the bard, is to tell him that you're gathering material for an adventure novel on the second timed dialogue, rather than mentioning Ermion.
- If you have trouble finding the pearl divers, they're hiding in an underwater cave from the island just underneath the boat.
- To solve the puzzle, the mirror which receives the beam of light from orb, should be turned right to redirect light on the second mirror. The second mirror should be moved to reflect it onto third, which should reflect it onto Philippa Eilhart.
- It is better not to exit the caves after finding the sun stone from where you entered. There are plenty of loot chests on the other exit side.