The Number of the Beast
Launchpad of World as Myth multiverse
Narrative Synopsis
Zebediah Carter, Deety Burroughs, Zeb's wife Hilda Corners, and Deety's father Jacob discover the "continua device", a mathematical mechanism that allows a vehicle to travel through six dimensions (three space, three time) to reach any of 6^6^6 (10,314,424,798,490,535,546,171,949,056) parallel universes, including worlds created by literature and fiction.
Fiction is simply history that hasn't happened in this universe yet.
Notable Passage
Historical & Editorial Context
Linked Heinlein's universe with those of L. Frank Baum (Oz), Lewis Carroll, and Edgar Rice Burroughs.