"Portals. We generally don't get more complicated than that. Doors, often literal, more common if you're talking about going by way of a jumper that you either found or happen to have on your payroll." The kettle whistles its readiness, and Gold takes it off the heat, preparing two cups and setting his new mixture to steep. "And sometimes a curse -- that's usually the only thing strong enough to bridge into a world without magic; your common paths will usually lead to other worlds with magic only."