A portal in science fiction and fantasy is a technological or magical doorway that connects two distant locations separated by spacetime. It usually consists of two or more gateways, with an object entering one gateway leaving via the other instantaneously.

Accidental travel is a plot device used in fantasy and science fiction in which an ordinary person or a group of people accidentally find themselves outside of their normal place or time for no apparent reason. In Russian  fandom the trope is known under the term "popadantsy", plural form for "popadanets", a person who accidentally travels elsewhere/elsewhen. The Russian term bears ironical flavor, because popadantsy has become a widespread cliche in pulp science fiction. The accidental time travel trope is known as time slip. Other kinds of accidental travel include space travel (e.g., through accidental wormholes or other spatial irregularities), travel to an alternative universe or into an alternative history. A particular kind of effortless accidental travel is finding oneself elsewhere/elsewhen occupying someone's else mind.