I was actually thinking about motifs of Above and Below, and how this gets developed in science fiction in stories (or movies) with giant skyscraper buildings, sometimes so tall that the people in them have no sense of their bottoms or tops--but I was thinking those are just a variant of the /netherworld--this world--heavenly world/ progression. Instead of three states with a boundary, it's like you get a spectrum. ... i'm going to try to write this up coherently for a blog post for Apex.

... Anyway, by train of thought I was thinking of stories with an underworld, and that got me thinking of Journey to the Center of the Earth