Teleportation Circles are created through a powerful magic ritual. As part of this ritual, a key-phrase of seven sigils is encoded into the circle, making a unique signature. If one knows this sigil key, it can be used in a separate ritual to teleport directly to the circle the key is linked to.
Teleportations Circles were far more commonly used during the height of the Seven Kingdoms to travel between the kingdoms on important business. After Gristamere betrayed the other kingdoms, many commonly known circles were destroyed to avoid the possibility of goblins spilling out into the town square of Estwald, for example. In modern times, most circles are jealously guarded secrets, although some settlements still have public circles…generally well outside the city walls.