User:Fyrael/Portal

Sliders

Stargate

Warcraft dark portal

Diablo town portal

Portal game (duh)

Rick & Morty

List of fiction employing parallel universes

Portals, Authored by: Jennifer Harwood-Smith, The Routledge Companion to Imaginary Worlds

Exploring the Four Types of Portal Narratives

From Wonderland to Outlander, Your Guide to Portals to Other Worlds

Lev Grossman lists his 5 favorite magic portals in fantasy fiction

First instances of portal for each media type: The Blazing World?