Received from: Automatically after finishing The War Council.
Step 1: Talk with Philippa at her house
In order to learn more about the magic artifact, head to Philippa Eilhart's house (M15, 14). You will find here being massaged by one of her apprentices. When asked about the artifact, she will tell you to talk with the villagers.
Step 2: Talk with the villagers about magic places
It's worth to visit Skalen Burdon (M15, 11), who will tell you of a certain wizard who used to live in the woods. You can search the abandoned ruins and deserted crypts. The next villager is the innkeeper, who of course can be found in the tavern (M15, 1). You will once more hear of the wizard, but this time you'll be directed to Cecil, who should know the most about Vergen. From the elder himself (M15, 12) you will also learn of the ruins in the woods - start your search for the magic artifact there.
Notice! It's worth to win with Skalen Burdon in dice poker twice. As a reward, he will give you the Dun Banner Cloak - it will come in handy in the future, during Death Symbolized.
Step 3: Find the place of power indicated by Cecil Burdon
Go through the gate (M15, 5), and use the stairs by the west gate (M15, 7) to head to the north gate (M15, 8). Right beside the river you will come across a dwarf and three Scoia'tael (M13, 4) members, eager for the reward for your head. Especially be careful with Todd, who is very resistant. You can first take care of the elves, while blocking the dwarf with Yrden.
Go to the right side of the river, where the water is rather shallow - you will be able to reach the other side. Slowly move through the dark forest and you will come across Kaedweni soldiers. Try not go in too deep, as you will be attacked by Harpies and further by lots of Nekkers. In order to reach the ruins, you have to run up the hill (M13, 5) and jump forward twice. You will be attacked by Harpies and the Celaeno Harpy. If you have a developed Igni sign, it might come in handy.
After eliminating them, climb up beside the ruins and take the magical crystal out of the harpy nest.
Step 4: Give the item to Philippa Eilhart
Return following the same path which you came here to minimize the risk of being attacked. Head to Philippa Eilhart's house (M15, 14) and tell her that you've obtained the source of power. The stone you have is a dwarf dream, which isn't strong enough. Geralt will mention that the Celaeno Harpy you came across is a dream thief.
Step 5: Convince Cecil Burdon to open the gate
You will learn that the Harpies have their nests in the old quarry. Unfortunately the gate is locked and the elder isn't eager to open it. The dwarf dream you obtained is in fact the dream of Cecil, so it's worth to use that fact and blackmail him into opening the gate. Head to Cecil Burdon (M15, 12) and after a short conversation you will receive the Runic key.
Step 6: Search the caves for the artifact
Notice! It's worth to take a look at the notice board and complete The Harpy Contract while you're at it.
Leave the city through the west gate (M15, 7). Head left on the crossroad with Scoia'tael and you will eventually reach the quarry (M13, 3). Look out for Harpies and Erynias - avoid running all the way down and try eliminating them in smaller groups. A developed Igni might come in handy. It's also worth to use Aard and Yrden, through you won't be able to drop the Harpies off the cliff with the first one. After reaching the bottom, you should note a large gate (M13, 6) leading to the Harpy lair. It can be opened with the key.
Notice! Inside you will have to fight the dangerous Celaeno Harpies. It's definitely worth having distributed talent points and a few bombs might also come in handy.
Right after going inside you will be attacked by two Celaeno Harpies. The fight definitely isn't of the easy ones - the rather small cave definitely makes dodging harder - be sure not to get jammed. All the spots at which Harpies appear have been marked with a red exclamation mark on the map (M16, !). They usually attack in groups of two-three. Your task is to gather the crystallized dreams, four in total. Their location has also been marked on the map in the guide (M16, 2).
Notice! One of the crystallized dreams is connected with Baltimore's Nightmare. you will learn of it only after reaching the projector.
Notice! Celaeno Harpies will appear each time you take a crystal.
Step 7: Watch the dreams from the cave on the projector and choose the most powerful one
Once you collect all four of them, approach the projector (M16, 3) and a cutscene will start during which one of the Harpies places a crystal in the projector. It's Letho's dream. After taking the crystal, you will be immediately attacked by the Celaeno Harpies Queen (M16, 4) aided by a few minions. The fight definitely won't be of the easy ones. Above all don't let them surround you, use the cave corridors to go round and eliminate the harpies one after another. You won't make it far without Quen here, though Yrden might also come in handy.
After a long and exhausting fight, approach the projector. Use it to play dreams from all the crystals you've collected.
Notice! Among the crystals you will find Baltimore's dream, which will start the Baltimore's Nightmare side quest.
Apart from Letho's dream, you will also see Baltimore's dream, Peasant's dream, Dragon's dream and Iorweth's dream, with the Dragon's being the most powerful of course. You can leave the nest (M16, 1) and head to Vergen, where you can give Philippa (M15, 14) the crystal.
Prize: 1000 XP