Within the dungeon settings of the Greyhawk campaign were areas that removed play to exotic places of water, wilderness, sky castles, and strange planes. Portions of the underground complex contained labyrinths; others led to caverns, unexpected places of beauty, dark temples, and so forth. In one place there was much combat, in another none, in a third a mixture of fighting and activities requiring thought and investigation. Outward and downward and elsewhere the delving adventurers went, and still they could never hope to know the true geography of that strange place.
Around that deep place of danger and the unknown sprawled both wild land and the teeming metropolis of the city. Those readers familiar with my Gord the Rogue stories will know a bit about the City of Greyhawk. Cosmopolitan and rude at once, its towers and catacombs offered as much in the way of derring-do as any dungeon could. Espionage and politics were there aplenty, all alongside simple taverns where thieves held concourse. Other cities and towns near and far beckoned. A whole continent filled with wonders of man and nature, kingdoms and despotic realms, and savage places too.
Beyond that world were the infinite places of the sort most humans of that milieu could not reach–except for the bold adventurers. These were the elemental planes and those connected to them, shadow and the ether. The multiverse extended below the realms of darkest evil, above the palaces of light, and laterally to the home of uncaring chaos on one end and absolute order on the other.
With all of that, and a co-GM too, there occurred from time to time a slackening of interest because one group or another simply had enough immersion in the realms of fantasy, magic, and make-believe. When that happened, a quick shift of gaming milieu would enable play to move to another adventure better suited to the player mood. The Old West, a brush with some World War II events, an expedition into New York City, an inadvertent transportation to a Starship, or a similar trip to some setting conceived by an author such as Edgar Rice Burroughs or Jack Vance–anything was possible.
– Gary Gygax, Master of the Game, pp. 89-90