Talk to Avallac'h, he will be upset about how you endangered Ciri... nah just kidding he will be overjoyed, at least as much as you can expect from an Aen Saevherne, for what you did on Bald Mountain. He will inform Geralt that his victory over Imlerith made him believe that they may have a chance at victory after all. He will propose getting rid of the other 2 generals starting with Ge'els, although not killing him but instead convincing him to stop supporting Eredin. Ge'els was loyal to their previous King Auberon Muircetach whom Eredin poisoned, thus the plan is to bring Ge'els to Corinne Tilly to show him what really happened to his King. But first Geralt has to find him thus he will have to travel to Tir ná Lia. After everything is explained you will have the option to head out immediately or tell him to wait at the location of the portal to other worlds which he found. The portal is in the house where you met Sarah, go to the basement and destroy the wall if you have not previously and approach the portal.
After entering the portal you will appear in a desert world, Avallac'h will tell you that there used to be an ocean there which was "alive" and not in the sense that it had fish in it. After a walk you will reach the next portal, however you have to wait for it to open, while waiting you will be attacked by Sandcrabs so kill them. Once the portal opens jump in and you will move to the next world.
Note: This is your only chance to get it so don't leave without it.
There will be poisonous fumes all around that will choke Geralt to death and Golden Oriole won't help here. You will have to run through them fast and take breaks on higher ground. After passing 2 poisoned areas you should reach the Place of power which will be around the corner to the right. Now from there move north which is opposite of the direction to the portal, but you will reach lower ground, pass another poisoned field and look to your left. You will see rocks that look like pillars and another poisoned field and higher ground you need to reach. Now move in the direction of the portal past the next field and you will be able to climb much higher, you will know you are in the right place as there will be a large skeleton in the next field when you reach the top. Run through it to reach the next safe spot and the portal should be within your reach. Just pass one last field and you will reach it, enter it to reach the next location. You will end up underwater, however the next portal will be very close so swim right into it.
Geralt will remark how cold it is, after a short walk you will find an ice wall, break it with Aard and move out. The cold is so intense that Garalt will be freezing and taking damage, so you have to be swift, Quen helps here, however if used while Geralt is already freezing it will break instantly. White Raffard's Decoction also helps, as do bonfires that you can light up with Igni when you find them. You will probably notice a lighthouse in the distance which is obviously where you need to go. When you reach the town you can use the houses to hide from the cold. Along the way you may encounter Hounds of the Wild Hunt or not depending how you proceed. When you reach the lighthouse you need to enter the basement instead of the lighthouse itself there you will meet Avallac'h again who will explain a few things. After you ask everything move on to the next portal.
Tir ná Lia
At last you are where you wanted to be follow Avallac'h to find Ge'els. He will be painting an elf girl in a particular style, once he notices you he will do a short conversation and agree to come with you. After witnessing the dream Ge'els will agree not to aid Eredin when the battle starts and tells them how to lure him into a trap using the Sunstone, after that Avallac'h helps him to get back to Tir ná Lia and the quest ends.
- News that Ciri and Geralt had defeated and killed Imlerith reached Avallac'h at once. I don't know how this happened, exactly, save perhaps that quickly learning of such things is the very essence of being a "Sage."
- At any rate, a wild notion possessed him. What if they could now sway Ge'els, one of Eredin's most powerful allies? What if they could bring him over to their side? A key general and advisor, Ge'els was the individual Eredin relied on for reinforcements. For his plan to work, he would need a dreamer, so Triss pointed him towards Corinne Tilly in Novigrad. Thus, by the time Geralt and Ciri rode into town, everything had been arranged. Now all they needed was Ge'els...
- To reach him, Avallac'h and Geralt would need to travel to the land of the Aen Elle, a voyage that would involve interdimensional travel, which in turn meant a whole lot of teleporting. Geralt vomited a little in his mouth and prepared to face the music.
- An unpleasant surprise was in store for Geralt after he departed the Ddiddiwedht Desert: Avallac'h was no longer with him. The Sage had warned him that something of the sort might happen, but Geralt had quietly hoped this would not be the case. His hopes had been misplaced, and now the witcher would have to stumble blindly and alone as he searched for the passage to the next world.
- Ah, what I wouldn't give to see with my own eyes what Geralt saw in the worlds he traversed. Yet most intriguing of all seemed the world of the Aen Elle, the end point of Geralt's and Avallac'h's journey. To behold the glories of this ancient elven civilization... but alas, fate granted this privilege not to a poet but to a witcher, who returned not with paeans to the distant world's beauty, but with a general of the Wild Hunt - one Ge'els. I must be fair, however, and state that the general proved useful.
- Avallac'h decided to bet all on the ace he had tucked up his sleeve. With the help of the dreamer Corinne Tilly, he proved to Ge'els that Eredin had killed Auberon, the erstwhile king of the Aen Elle and the object of Ge'els' undying devotion.
- Confronted by this revelation, Ge'els could hardly return to business as usual. He struggled internally for some moments before revealing the one way Geralt and friends could hope to defeat Eredin and company. They would have to battle Eredin and the Hunt in their own world and on their own terms. The first step - to use the Sunstone to summon the Naglfar. A plan of action was devised - Geralt, Ciri, the sorceresses and Avallac'h would sail to Skellige to find the stone, while Zoltan and I would stay behind in Novigrad to keep the hearth fires burning and secure our friends' return.
- Join Avallac'h.
- Follow Avallac'h.
- Find the next passage.
- Wait until the passage opens.
- Kill the monsters.
- Travel to the next world.
- Find the next passage.
- Find the next passage.
- Get to the lighthouse.
- Travel to the next world. (500 )
- Follow Avallac'h.
- Talk to Ge'els.
- In the second world there is an Aard Place of Power.
- Lighting the fires in the Ice Plains will regenerate health.
- The Quen sign and Superior White Raffard's Decoction damage absorption will protect from the frost, though both will deplete quickly.
- If one is looking for a way to level up Aerondight, the desert is a great place to do it, provided the player is strong enough to quickly kill the sandcrabs and avoids being hit (or makes ample use of Quen) as they will spawn indefinitely until Geralt goes through the portal.
- The same cannot be said about the Mutagenerator. The sandcrabs will not count as charges to produce mutagens.
- According to Avallac'h, the desert world used to be populated by a sentient, living sea. This is a clear nod towards the science-fiction novel Solaris by a Polish author Stanisław Lem, which centres around human interaction with such an alien form of life.