The only way to get into or out of Sigil is through a portal. No other form of teleportation or planar trawl can penetrate the barriers around the City of Doors.
Once you’re in Sigil, you can move around the city with teleportation powers, but you can’t enter or exit the place except through the portals that dot the cityscape.
A portal. also called a gate. can be any aperture or bounded space, Windows, doors, archways, sewer grates, large crates or chests. pits. trestles. hearths-all these opening and more might be portals in the City of Doors.
Some portals remain constantly active, meaning that all you have to do to use them is to step through one. Many portals, however, require a gate key to operate. Without the proper gate key. a portal is just a space. and a mundane space at that. With the proper gate key, a portal becomes a gateway to someplace else. A gate key usually takes the form of an object, from an actual key to anything else that can easily be carried on your person. Sometimes. however, a gate key might be a spoken word or phrase, a gesture, or a particular state of mind.
Portals can be permanent. temporary. or shifting. There’s something about Sigil that seems to attract randomly occurring portals that wink into and out of existence without any apparent rhyme or reason. These randomly occurring portals can appear anywhere and last momentarily or remain open for days or weeks at a time. An expensive ritual can shield areas from the incursion of random portals, but only the most well•to-do neighborhoods in Sigil can afford to keep such protections in place at all times. Portals tend to be two-way. If you step through a portal, you can usually step back the nay you came. You might need a gate key. but otherwise a dour is a
door. There are some rare portals that go only one way. Usually. the truth is that a different gate key is required to make the return trip. so it really isn’t a one-way door at all. Or the portal winks out or moves before you can step back. But sometimes. you might run into an actual
one-way portal—and going through such a portal might leave you in a very bad place indeed.