A portal is an opening in the walls of a building, gate or fortification, and especially a grand entrance to an important structure. Doors, metal gates or portcullis in the opening can be used to control entry or exit. The surface surrounding the opening may be made of simple building materials or decorated with ornamentation. Elements of a portal can include the voussoir, tympanum, an ornamented mullion or trumeau between doors, and columns with carvings of saints in the westwork of a church.
Portals in science fiction allow rapid travel between distant locations, often originating from some combination of natural phenomenon and technological device. These fictional devices are required for most stories on an inter-solar scale, otherwise transit time would be excessive for storytelling purposes. An advantage of portal technology over a faster-than-light drive is that it can be imagined to work instantly, and can travel to the past or future. In other forms of fiction, a portal may be magical, and connect to an alternate universe or plane of existence.