Humans as Burrowers

"A handful of religions have imagined underworlds that are pleasant or strange without being frightening, but they’re the exceptions. In most mythologies, going down is not a good thing—it’s a quest, a challenge, a trial. No one visits the underworld for a picnic."

Curious what you would make of my take on Annwn, for my Ravenstone book. There were mixed accounts in the lore about Annwn, some said it was underground, others said it was an island. So I made it an island in an underground sea. There's something similar to sunlight, but there's no direct connection to the surface, except those caused by erosion. The people who live in Annwn tend to plug those up pretty quickly, though, because the surface of the planet is a Lovecraftian nightmare.