Portal

Portals allow residents of The Hollow to travel instantaneously from one location within it to another. Of course, the Hollow need not obey the laws of physical space, including the idea that one must physically move from one location to another -- technically, every door in the Hollow is a portal that opens from an "exterior" instance of reality to an "interior" one. However, most inhabitants of the Hollow find the idea of not following some kind of environmental continuity quite confusing; when, in an early test version of the Hollow, users were granted the ability to move themselves freely from one space to another, they struggled to control this power, and often used it accidentally. Thus, portals have been codified into a system of clearly-designated objects and spells that makes sense to the average resident of the Hollow.
There are two types of portals in the Hollow: standing portals and temporary portals. Standing portals exist as objects in the Hollow, usually as some kind of frame that a user can step through to reach their destination. Sometimes this destination is another standing portal and sometimes it is not; in the latter case, the standing portal may or may not open a temporary return portal at the destination. Most standing portals include control modules that allow a user to select a destination from multiple possibilities, though there are also standing portals that always link to the same destination, usually another standing portal.
Temporary portals may be activated by objects worn on one's person, often an amulet or other piece of jewelry. Magically skilled individuals may also simply "cast" the portal as a spell-like series of gestures and intent, a practice often used by Architects. This can go awry if the caster loses focus or fumbles a gesture, however, so object-based portals are more popular. Some portal-activating objects always lead to the same destination, while others are more versatile and may accept input to determine where the portal should lead.
Creating new portals and portal objects is a common practice activity for apprentices in the Architects' Guild. Standing portals are considered more basic than temporary portals, while spell-portals are the most difficult to conjure.