From publisher blurb:
Rules for settlements and PC constructed kingdoms appear in the Pathfinder Roleplaying Game: GameMastery Guide and Pathfinder Roleplaying Game: Ultimate Campaign. These provide all the information required for the construction of most normal communities, from discrete little thorps to complex thriving nations. However, there is a distinct lack of the wondrous and fantastical within. The rules fall short when posed with the challenge of fashioning technomagical civilizations stuck out of time, necromancy-saturated cities built on undead labor, or extraplanar nations united by mysterious magical gates.
Naturally, it seems that the founding of such should be beyond the reach of mere mortals, but the Pathfinder Roleplaying Game: Mythic Adventures book allows PCs to achieve greater reaches of power. Likewise, the GM may simply wish to establish a campaign visiting or based within a location touched by mythic influences. Four Horsemen Present Mythic Kingdoms attempts to provide GMs and players with the tools necessary to build castles in the sky or reclaim a lost legendary realm steeped in destiny.