>What would be the equivalent of B5 in a fantasy? A floating sky island? A neutral world in a multiverse?

Imagine a typical fantasy setting in which humans live amongst other races - elves, dwarves, goblins and the like (but substitute them for aliens, the archetypes are mostly the same) Humans are still venturing out into the greater world and were nearly being wiped out in a war with the elves (Minbari) when their intitial meeting went poorly. Humans create a city called Babylon where representatives of various races could come together to talk, trade and interact peacefully at the outer boundaries of what humans knew to be "the world," near the countries of wild magic where eldritch and ancient things were known to dwell, which even the older races fear to speak of.

The fourth Babylon vanished without a trace. Humans have barely begun to master even the simplest of magics but this is far beyond their understanding, and the elves, who always seem to know more than they say, say nothing. But, humans being perhaps too stupid or prideful to know when to quit, simply built it again, and tried again.

But there are prophecies of an ancient enemy called The Lords of Shadow which have slumbered deep underground for so long that they have become mere legend to all but the oldest races, if not forgotten altogether. A profane force of the deepest and darkest magics which was beaten back by an alliance of older races and the Lords of Light, the divine high elf mages who still watch over the younger races and regard humans with bemusement.

Or they seem to. It's hard to tell with them. Their faces are always obscured by masks, and everything they say is a riddle.

The prophecies say the time is drawing near for the Lords of Shadow to awaken again, and the dark magic to return... and strangely enough, within this city where humans, elves, dwarves, angels and devils all walk amongst one another, the key to the fate of the world and the coming of the New Age may be this weak, naive, plucky race called humans, whose nature seems to stand between the darkness and the light, and in whom the Elves have taken a particular interest, for reason they refuse to reveal.

It really isn't that difficult. Not every element has to have a precise 1:1 match, so many of the themes and motifs are right out of fantasy. You have an ancient immortal named Lorien, a mysterious broker of dark wishes named Morden who serves the Shadows, a group of elite warriors called Rangers who trained under the Elves (Minbari) and fought in the last great war against Sauron-sorry The Shadows. The Technomages are literal space wizards.

You could do some Norse Mythology thing and say "hyperspace" is a magical form of travel between the "realms" of these various races, and have the story take place when humans have just discovered the magic that allows access to the world tree. Add a Tower of Babel analogy and say the city of Babylon already existed and was already a place where different races commingled because it's where the portal was, making it both an international and interdimensional hub, but one day the old Tower of Babylon (which is where the portal is) just disappeared (probably those damned elves) but they built a new one.