Interplanar Travel

Many stories that feature multiple
worlds assume that travel between
those worlds is a one-way trip:
unlucky (or lucky!) travelers somehow
fall through the gap between worlds.
But regular travel between worlds is an
interesting possibility, as it lets explor-
ers study, exploit, and perhaps even
conquer entire worlds. In this case, the
most important question to answer is,
“How do the adventurers get there?”