What is a Realm?
A realm is a small area of land, from a few square miles, to hundreds of square miles, with its own unique rules. The idea is not dissimilar to the concept of planes in vanilla D&D, but on a much smaller scale. The borders of realms are always different, but they are invariably there. No realms are infinite—some drop off into great abysses, others have walls of light, or mist, or stone. Some have endless oceans that seem spread out forever in every direction, but sailors quickly find themselves back at port. Realms are often classified by their size, the smallest being known as ‘fields.’ The largest are called ‘worlds.’ In between are ‘circles’ (not always circular), ‘cantons’, ‘domains’, ‘territories’, and ‘provinces.’
How do you travel between realms?
Most commonly, travel between realms takes place on a magical device known as a Grand Scale. The Grand Scale (or Scale) is a large device for weighing people and objects in two realms simultaneously. They are very large equivalents of scales that most merchants use to weigh their wares, and their appearance varies from realm to realm. They serve to ensure that the transfer of mass between realms is kept near constant. The Grand Scales are almost entirely under the control of The Adversary, who is credited with their invention.
Let’s say you were to travel between the Territory of Constance, and the Field of Muir. In both places there is a Scale that is tied to the other place. Put a weight on the Scale in Muir, and the Scale in Constance will shift appropriately. When the Scale is balanced, the operator of the Scale can swap the loads in both realms. You appear in Muir, and a weight equal to you appears in Constance. This is most often other travelers, but it could just as easily be ballast.
Minions of The Adversary have built a highway of sorts that travels between most of the central realms, and built out roads into the frontier realms. They carefully control trade and travel between the realms. If a realm fails to pay its taxes, the Scales in the realm are often disabled after a particularly nasty creature is sent through, leaving many trapped in a nightmare.
It is rumored that other methods of travel between realms is possible. Some creatures appear to have the ability to move between the realms on their own. Some say the Dwarves have dug tunnels and emerged in new realms. Seafarers tell tales of being devoured by a storm, only to wreck in a new realm. These rumors are as ubiquitous as they are varied – ask fifteen people about it, and you’ll get thirty different responses.