Implication makes your world feel vast and complicated. It paints images in the reader’s periphery, giving them an idea—a generalization—that’s just enough to fill in the blanks without spelling out the exact formula.
It’s smoke and mirrors, hand puppets making shadowy shapes on the wall. That’s the Imperiator’s Sanitarium, and you never want to go there. Why? Because we’ve seen someone refer to it with fear, or maybe someone who went in came out different. We don’t know what the Imperiator is doing in there, and we don’t need to. All we need to know is that it’s bad.
That’s just one example, but there are tons of other ways you can fill out your world using little details—each one hinting at the wider world without explicitly saying it.
An organic world has constants that affect all its denizens. These are things like trade, religious institutions, markets, etc. These elements can be littered throughout your world and have small levels of influence on your characters. This will imply that there’s a larger organic world, one that has its own ebb and flow outside of your narrative. This can be done with little bits of detail sprinkled throughout your story. A mention of trade routes, or how two different people view a religious institution, little moments that not only build character but fill out your world.
Keeping details vague can make your world feel bigger. Give them just enough to fill in the blanks, a few guideposts here and there will allow them to populate the roads with their own speculations. If we look at the above example, the Imperiator’s Sanitarium, we don’t need to know what they’re doing in there. Long descriptions of their experiments/torture/whatever will narrow the walls of your reader’s view. They’ll feel boxed in, and everything will start to lose its sense of scale. Leaving things vague, only giving hints of what happens in the Sanitarium and showing the consequences, gives room for the reader to fill in the blanks with their imagination.
The key is to convince the reader that there’s a whole lot of shit happening behind the scenes that they don’t know about. There should always be a sense that there’s more to learn, more to discover.
Small street level elements can add a lot as well. Things like magic lanterns, the way buildings look, or those crow/rat hybrids that are all over the city. This can take pre-established worldbuilding elements and show the readers how they’re integrated into the world. Necromancy is cool when the secretive underground cult is chanting and ohming, but it can also be dotted throughout the world. Maybe detectives raise the dead to ask them questions, or people make a wish when they see a roving spirit. Really, these elements can be integrated any way you like, but having them be constant, as well as showing how they affect the grander world—not just your plot—goes a long way in making the world feel expansive.
The local lingo can show how your world grew organically. If your denizens worship a fire god, then maybe they shout burn me! as an expletive. Language can play a huge role in cementing the believability of your world. The names of people and places should have a sense that they share an etymology, or if they don’t then maybe that’s also a worldbuilding element. If all the people/locations have monosyllabic names like Grot, Kur, Fin, and so on, when Ezekael shows up, we know he’s a stranger from a foreign land.
But don’t go overboard with made-up words, they should be sprinkled throughout the story. Too much all over the place can make your story unreadable (Mad Max gets away with this, but its lingo fits into the degraded sanity of the wasteland).
These are just a few ways to make your world feel big. Each, on its own, seemingly a little detail, but together they create a cohesive and evocative image. Give them try and let me know how it turns out!