Try as I might, I can’t find any sources that definitively link the “Upside-down” world of the show _Stranger Things_ to early Scandinavian myths about the land of the dead, but there are so many similarities it seems hard to believe that the content creators weren’t deliberately borrowing.
To take the words of ethnographer Tim Ingold, in pre-historic northern Scandinavia, where it was thought that the underworld was a mirror-image of the land of the living, “the lower layer [of the cosmos] is the inverted world of the dead, whose feet, since they walk upside-down, are sometimes thought . . . to touch the soles of the living who walk upright.”. Icelandic myths tell of the need of the dead to wear “hel-shoes” so that they can properly traverse to their new realm, which is often associated with the sea and water.
In pre-historic rock art of Bohuslän, Sweden, the landscape reflects these ideas. As excavated and discussed by archaeologist Richard Bradley, the rock art dating from 1800-500 BCE would have shown a horizontal line of boats, interspersed with the outline of perpendicular footprints — all this symbolized a path which cut across “the landscape of the living and linking two distinct domains: the higher ground, the ‘heavens’, where Bronze Age barrows celebrated the ancestors, and the sea of the dead to which they had to travel” (with the footsoles representing the hel-shoes as a kind of directional portal).
The 17th-century English mystic Thomas Traherne poetically captured this imagery in his “Shadows in the Water”:
By walking Men’s reversed Feet
I chanc’d another world to meet;
Tho it did not to View exceed
A Phantom, ’tis a World indeed,
Where Skies beneath us shine
And earth by Art divine
Another face presents below,
Where People’s feet against Ours go.
Sources: Pp. 142 and 144 of _An Archaeology of Natural Places_ by Richard Bradley, Routledge, 2000, Art by the Banyan Tee