Editing Skein of Worlds:The Material Plane (section)

=== Portals ===
The simplest way to get between two spheres is through an open portal. You can clearly see what's on the other side and simply step (or ride, or sail) through. Finding and opening a portal though is no simple task.

Portals are ancient artifacts of unknown origin. (Actually, they have many origins, but few people know much, if anything, about them.) A portal links two places somewhat like a ''gate'' spell. There are many portals in existence, but most are hidden, locked or both. The key to a locked portal can be any number of things from a specific item to a time of day or year to a particular bloodline. Unlocking a newly discovered portal can be very difficult since there is often little to no information as to the portal even existing, much less when it was made or what it was used for. 

Not all portals are locked though. Even though they may always be open, they still might be very hard to find. There is no distinct boundary between one side and the other. Light, sound, objects and even magic pass through unhindered. If there is no way to look around both sides of the portal (where one might see two different views), there's really no physical way to tell where one side begins and the other ends. Even magical means rarely work. Normally, ''detect magic'' would cause a portal to glow brightly (even blindingly so); however, most portals were built with enchantments to prevent such simple spells from working on them. (This could have been done for any number of reasons, and likely varies from portal to portal.)

Though rare, there are some large, always open portals out in the open. These tend to become important centers of trade between the two planets they connect. Assuming the portal is built on suitable terrain (and sometimes not-so-suitable terrain), the area around it is likely to grow into a fairly large city spanning both sides of the portal. (Portals on suns and black holes exist, but are even rarer than portals on planets. Large, always open portals on a sun or black hole are basically non-existent for a number of reasons.)

Finding and unlocking a new portal and charting what's on the other side can be a great adventure, or an even greater business opportunity. This is another reason why many portals remain unknown. Their finders may not want to share the secret, eventually taking it to their grave. On the other hand, many such secrets are passed down from father to son, or master to apprentice, so some portals that may seem undiscovered might just be well kept secrets.

Portals are always built into either a natural or artificial structure. All known portals are immobile and it is theorized that moving one would be a bad idea.