How would portals that link Earth and a fantasy world work?

Question

I don't exactly want the science on how portals work (though I wouldn't complain if someone did), but I suppose they would work lore-wise. Portals can often be found behind long forgotten entrances, such as behind the doors of an ancient mausoleum.
The portals themselves are invisible and often unusable, meaning most people will pass through one without knowing that they did. The portals usually are only able to be used by things from the fantasy world, because what the portals try to do is to separate things from the fantasy world and Earth. But because the majority of the things from the fantasy world's ancestors come from Earth, the portals get confused on whether they belong on Earth or the other place, so they end up just being able to transverse them without any problem. The only exception are semi-intelligent gremlins, which can teleport between the worlds without the need for portals.

The biggest issue I'm facing is exactly how things from Earth would even get to the fantasy world. For instance, an elf can travel between the two, because its ancestors came from Earth and and it was born in the fantasy world. But how would said ancestors even get to the fantasy world? I was thinking maybe things that touch the gremlins while they're teleporting back to the fantasy world teleport along with them, but this is kind of underwhelming.

Note: Gremlins are the only things that are proven to not come from Earth. And I'm okay with any answer, as you can guess I'm pretty early in the process so currently nothing would really break the rules in my universe because I haven't really established any.

Answer 1

I'm thinking back to the old Irish tales.

The changeling was a creature found in place of their own dear child by its parents, the baby having been stolen and replaced with an imposter. (Perhaps a Gremlin, perhaps something-else from the other world.)

The act of stealing an Elven baby and replacing it, created a new balance between the worlds, where before, only Gremlins could flit between the two, the presence of a "foreign body" in each world facilitated a new link between realms.

Feeling a constant pull towards their true-homes, acting as a two-way anchor allowing a passage to be created, the kidnapped elf and replacement creature were then able to create a portal back to their home-grounds. With both portal entrances created - one from each side- travel could begin.

Even with all back in their right place, the portal would still function, like picking a scab to keep a wound open, even if not picked for a while, the scar would still be there to be opened with a sharp poke.

Answer 2

I think you are correct in thinking that Gremlins are the key to the answer, as they are the outlier as far as being the only species having this ability to travel without portals.

Maybe the Gremlins' ancestors used to be more advanced than they are now, and willfully travelled between the worlds for fun and profit, often mixing with early humans and, although officially frowned upon, occasionally mating, with unpredictable results. Some of these babies were born with pointy ears, some with horns and hooves, some were green and fanged. A few were lucky enough to be close enough to human or gremlin that they could pass for normal, but most were shunned and ostracised.

Eventually, those in charge decided that enough was enough, allocated earth as off limits, relocated the half human freaks to a new world and forgot all about the whole mess.

Millennia later, the Gremlins have regressed to semi-intelligence due to wandering down an evolutionary cul-de-sac, but the freaks have thrived, evolving into the different races in your fantasy world. Being half-human, they don't have such a strong ability to cross through into our world and back as the Gremlins, but if they can find a suitable weak spot they can sometimes break the barrier and cross.

This gives an opportunity for a human character to find out that they were also descended from a human/gremlin hybrid, albeit one that was passed off as human and missed the last boat to fantasy world. They can also pass through the portals.

Maybe others can, too..

Answer 3

Cats

Cats find gremlins delicious, and try to eat them whenever they can. This often leads to cats being transported to the fantasy world when the gremlin tries to teleport away. As such, most cats count as supernatural beings. They often know the locations of portals, and will head over to them to try and hunt more gremlins to eat.

Any human in close proximity to a cat can pass over. If they chase down their cat to see where they went they might end up in another world.

Answer 4

I'll offer you two examples, one from D&D and one of my own.

Planar Worlds

If you ever read the planar setting for Forgotten Realms, all the different planar worlds are interconnected by the Astral Sea, a silvery between world realm. When one projects themselves to another plane, they are connected through a silvery cord. Few things can sever this cord, such as a githyanki's silver sword. The Githyanki is a race that lives natively to the astral sea and has the means to quickly traverse to different planes.

Your gremlins could model some ability after that of the githyanki.

4th-Dimentional Axis

I'm building two different worlds, one sci-fi and one fantasy, and because I really like medium-hardish science and hard magic worlds, I like to incorporate some scientific elements to my fantasy world and might someday try to link them while maintaining consistent rules between worlds. This has inspired me to consider that different planes are actually worlds linked to ours on a 4th-dimensional axis.

Part of this was inspired by a clip from YouTube's Action Lab. If you have a 1-dimensional world, that is, a line, inhabitants of this 1D world can only traverse from one end to the other by the distance of that line. However, in the 2D or 3D world, we can fold the line over and let the two ends meet.

If you draw a circle and a character on the same piece of paper, from the perspective of that 2D character he can only go two-directions to get to the otherside of the cirlce. However, as a 3-dimensional being, you can fold the paper and place the character on the other side of the circle.

Likewise, for us 3-dimesional beings, there may be ways to traverse or "teleport" to different locations through the 4th-dimensional axis, even if we cannot physically perceive this.

I plan to use this to explain teleportation and portals in my world. 4th dimension is not a "world" as bad old school sci-fi like to use. 4th dimension is an axis that can be traversed through. For paranormal phenomena, perhaps it is a result of an event from 4th-dimensionally adjacent world that is somehow bleeding into that of our own.

I don't have gremlins in my world, but perhaps they may naturally have the ability to perceive that 4th-dimensional axis, just like some humans are tetrachromatic and can see colors that most humans physically cannot perceive.

Answer 5

I think a way you could do it is that for the specific fantasy world being traveled to, the person from earth can travel there because that specific fantasy world has some kind of strong connection to them. Maybe much of the world is arid, and they grew up in Arizona, and are now living away from home, feeling a yearning for that again.

Maybe an artist feels a draw towards a fantasy kingdom focused on celebrating many mediums of art.

Obviously this would be far, far more rare than normal travel between the worlds - but it's just the kind of thing you can justify to get a protagonist through.

The thing I find interesting is that this would then allow the traveler from Earth to easily return home, in contrast to a lot of portal fantasy/isekai. One could then perhaps make an "anchor" of sorts in the fantasy world to fix the connection there - maybe join some cause, find some good friend or lover -

Then the person would have a connection to both worlds, and could travel somewhat easily between them. You could even then bring the person you've become friends with to earth, as they now have a connection to earth by proxy through you (and of course there would be diminishing returns on this).

I could see a lot of interesting stories growing out of this, where someone's connection to the fantasy world becomes so affixed, their interest, connection, and therefore access to Earth begins to wane.

Hope that I'm not super misunderstanding your magic system here, hope that I provided some help.

Answer 6

Gremlins taught humans how to cross

Perhaps voluntarily, perhaps by accident. Possibly both. Do Gremlins travel by using some innate power/aptitude, or do they have their own magic/method for crossing? If it's the latter, couldn't some humans somehow have learned their tricks and secrets, and then travelled back?

Some humans inherited the ability to cross

Alternatively, as others have suggested, if elves and other fantasy beings are the offspring of humans and Gremlins, could some of these half-humans have inherited this magic somehow?

Depending on your setting, it could happen that proximity to Gremlins could be enough to enable Gremlin-like abilities that could let humans cross to this other dimension/world.