Only people who have watched the show will know what I'm referring to and I don't think mentioning this one thing constitutes a "spoiler", but I've been re-watching Stranger Things and I think the "Upside Down" is a good analogy for the inside of the body. Both are dark, mysterious, unknown as to what's really happening (or not) inside of them at any given time, vein-like network like in the human body, etc. Both are closely linked to the outside world.