Minecraft wiki entry for Building_a_metropolis, associated text: Ecumenopolis: Turn the whole world into a ecumenopolis (read: an extremely big city), stretching from bedrock level to the world height limit. At the top, there could be high-rise penthouses with panoramic windows, while at the bottom, there are slums and gang headquarters. If you have limited time or resources, you can skip the underground part and just make your city a colossal skyscraper. Regardless of how you do it, this project will be very time-consuming in Survival mode, and even in Creative mode will take quite a while.