I wrote a very short children's story a couple years ago where my characters traveled to different worlds. Here is a list of the simple worlds they traveled to (again, I was about 8, so not as advanced as I am now. No offense meant to anyone who is 8):

WORLD 1: Fantasy. I based it off of Winx club so I actually called it the "Magix Dimension" at the time. You can make your fantasy world with however many speicies you like!

WORLD 2: Minecraft. Think of a video game your characters play. If you aren't planning to publish, you can make it a real game. Many games are pixelated, so keep that in mind.

WORLD 3: Medieval times. Pick somewhere in history. If it's not a realistic world already(besides the traveling to different worlds thing), you're out of luck.

I had a page and time limit, so I didn't include any other worlds. Oh, I just thought of something. If your world is not realistic, for history you can travel to the future and for fantasy you can travel to the realistic world. Sorry that I only came up with three. A lot of the Rps and solo writes have great ideas as well, so you can check those if you need more ideas.

Yunse, writing come to you, and good luck!

unsuspectingstrytllr 

PS. The language I wrote in does not exist. Just a made up word. 

My advice is to have just a few fundamental laws of physics, or else of magic, that are true throughout all five worlds (i.e. matter/energy cannot be created or destroyed, there's no bringing anything back once it's dead, etc.). For someone to be able to travel between them, they have to be connected in some fashion, even if it's very, very loose, like sharing the fact that gravity works the way it does IRL (or something like that).

Other than that? Go wild. Do try, though, not to have the worlds be singular tropes, but a richer patchwork of different attributes. A few ideas for such attributes I had:

-ghosts exist, and can be summoned freely, though they can't interact with physical objects

-time slips and stutters, either in people's perception or in the world itself (or both, for extra trippiness)

-dead magic: no ambient magic whatsoever; no one can cast spells, magic items are drained of power, creatures that depend on magic for survival will die

-foliage is some other color besides green

-there is always wind blowing in the same general direction; it can lessen to a breeze or worsen to a hurricane, but the air is never still

-everything is sentient, including "inanimate" objects

-the fabric of the universe is unstable, making portals easy but treacherous to open; they could easily grow too large and engulf things they shouldn't, or go someplace else than where you intended

-the surface of the ground is an arid, irradiated wasteland, but underground are vast caverns with entire cities in them

-there is a certain element (in the same sense as carbon or oxygen) that defies gravity, making objects containing it float

-magic travels through water instantly, a bit like lightning

-music is inherently magical; you can cast just about any spell with only a musical instrument, if you know the right tune

-the seasons do actually turn because of sentient influence- if we didn't do the right ceremonies to usher in spring, it would never come

-anime is real

-...okay, so that's more than a few, but I hope this helps :)

Walk around outside and think. Think of your favorite things, things that scare you, things that make you happy  or sad. Also draw it, just draw a quick map of what ever comes into your head while you are thinking.

Hope that helped,

June