I recently read the Long Earth saga by Terry Pratchett and Stephen Baxter. The story begins in the near future when an eccentric engineer anonymously publishes plans for a “stepper box” which takes the user to a parallel world, adjacent in a chain of millions.
It soon emerges that a few humans have the talent of Stepping without a box. In one episode, two of these (including an ancestor of a main character) help the Underground Railroad, provoking in me a question they did not ask: Rather than sneaking the escapees to Canada, what if we leave them in a side-world? They’d have to learn to live Paleolithic-style (metallic iron cannot be transported), but that life evidently was not so bad.