Because I’m somewhat masochistic, I’m thinking of the urban fantasy world that I’m currently writing in as part of a larger multiverse. In this multiverse, the great majority of worlds are variations on Earth. Currently, in my development process, there are:
Earth-000: Our world, baseline.
Earth-001: the world I’m writing in at the moment (unnamed)
Earth-002: Immortalis Mundi
Earth-003: Veiled Earth
Earth-004: Magipocalypse Earth
Earth-xxx: any future developments
Other worlds include:
Aethoth: a secondary, high-low fantasy world I’m placing in development
Ethirach: a secondary, high-ish fantasy world inspired loosely by Earth’s “lost lands” legends, ex. Atlantis, Mu, Ys, Shambhala (development on hold)
At the moment, travel between worlds in the multiverse is impossible because all the “doorways” were closed roughly 40,000 years ago (Earth-000 time). Time doesn’t necessarily pass at the same rate on each world. I think the ur-gate is located on either Aethoth or Ethirach (haven’t decided which). Reopening/activating that gate reopens the multiverse.
However, even with the “doors” open, direct travel between Earths will be impossible. Probably due to similarity. Therefore, all travel between Earths needs to go through Aethoth or Ethirach, ex. Earth-001 to Earth-004 can’t work, but Earth-001 to Aethoth to Earth-004 works just fine.
It’s something I’m playing with. I’m not entirely certain that will be the final form, yet.