The Vanished City
Until not long ago, the name of 'place' was improper for the Vanished City, since it was believed to be a mere legend.
According to it, somewhere towards the sunset and then far away to the North, beyond all mountains and mires, there was a small but powerful kingdom, guarded by nearly impassable mountains. The capitol of this kingdom was a city of unsurpassed grandeur. We shall not insist upon its description now. Enough be said that it was built on a tall island in the middle of a huge lake. Blue walls surrounded it thrice, on three heights. If the rest of its defences - the mountains and the dark blue, almost black lake, were natural or not - that is not known. Most likely they weren't. The only known ruler of the kingdom was the Mage-King Kayffa, who reigned for several centuries. Whether he was a human who had prolonged his life with the help of magic and sorcery, or some other being that had taken on a human shape, that no one had ever found out.
His power was founded on a terribly strong magic, so that three neighbouring kingdoms that had conquered many peoples were sending him yearly tribute, in gold, grains, ore, sulphur, precious tomes and children. The journey of the animal handlers of the caravans with these goods was always a one-way one. It is known of no person to have ever left the empire. The king's messages were sent by hideous birds the size of eagles, with strong blood red beaks and covered in grey feathers. A strange intelligence gleamed in their orange eyes and they always accomplished their missions faithfully. Only on a few occasions did the king himself leave his country and those who made him... weren't too happy about it.
What stirred the imagination of people even more than the mystery of his ascencion to the throne, was the immeasurable wealth he had gathered (and it wasn't only gold and gems, but rather a huge collection of scrolls, pergaments, spells, long-forgotten books and artefacts strong beyond any grasp), as well as the sudden end of the kingdom. One day, the hideous bird messengers ceased to fly, the
caravans carrying tribute found the great Guard Gates locked and deserted and no other sign was ever seen or heard of the Mage-King.
Some said, the City had sunken into the lake, others that the island was actually a volcano that had errupted, thus breaking the spell on which the kingdom was built. Another theory claims that the King had returned to the Plane of Existence whence he had come, together with the powerful artefacts gathered from this world and so the kingdom slowly faded, caught in the ring of surrounding mountains, though small communities might have survived hidden. There is also a whispered rumour that the King had met his end at the hands of entities from other Planes, that he mastered through spells, when he has summoned one beyond his strength.
In any case, all attempts to identify traces of his kingdom in the Mountains, or those of the Vanished City have so far failed. After centuries, people have started to forget the truth and consider everything a mere legend. It was told to children in long winter nights and adventurers dreamed of its fabulous wealths around camp fires. No one however still considered hunting jhe mirage it had become.
Drogo the wizard apprentice has managed to steal a map of the Vanished City from his former (presumable gone mad) master, an old piece of skind depicting the great city on its island and the placement of other settlements inside the mountain rings.
Based on that and on various other rumours and legends, the rogue Thorn has identified the place as somewhere beyond (or inside) the Spine of the World, the impassable mountain rage that borders the North of Portalia, as shown on the map below.