The Dying Age
Horizon is a magical city heavily influenced by the Archmage. It holds unparalleled libraries of arcane lore, wizards busy with mysterious tasks, rival arcane guilds competing in all ways, and, of course, many opportunities for the PCs to be recognized as exceptional individuals who can accomplish what the NPC wizards cannot.
While Concord has the high towers of the elves, Horizon depends much more on flying buildings and floating force ramps. Such constructs are probably a creation of the Archmage, and possibly channel tremendous magical energy once harnessed by the Wizard King.