A common feature in Scientifiction and Fantasy works are portals, doors / holes / oversized spinning stone rings which allow characters to get from point A to point B instantly (or after 3.2 seconds).
These are often one-way; once characters pass through, they can't go back.
Why is this?
NOTE: In my story, portals are a bit of a crossbreed between traditional fantasy portals and those in the Stargate-verse. They are magical in nature, but a specific type of oversized stone
ring square is required to create them. Also, while the "entry" is always wherever the not-ring is located, the "exit" can be created anywhere within a circular area of 100 miles from the "entry".
EDIT: In response to @JBH's very helpful comment, here is some more background information to narrow things down.
The way my magical system works is that there is a small amount of background magic which well-trained people (wizards and sorcerers, with the distinction between the two being as per this answer) can manipulate via spells (also per that answer).
Portals require significantly more energy than the normal background amount, and thus can be only created by sorcerers. Wizards technically have the ability, but they lack the necessary expertise in spell-scripting and manipulation of magic capacitors.
The range of portals is limited by the amount of magic required to generate and sustain them. It is conceivably possible to extend their range by drawing power from multiple crystal balls; however, nobody has been able to successfully do this.