There was a BBC documentary back in the early '90s about a huge community of people living in the sewers in Russia. There were some political dissidents, punks, heroin addicts and two nerds having a Satanist marriage ceremony down there. No Mayan squid-bats, though.
Didn't early Christian doctrine teach that Hell was literally in the Earth's core? Interestingly, St Brendan of Ireland sailed past Hell rather than katabasing (?) down there. According to him, it was a large volcano, with winged demons flying around above the vent. One of his fellow monks had a filthy thought and a demon swooped down, pulled him screaming out of the boat and flew back to drop him into the volcano. The survivors then met Judas Iscariot, stranded on a rock. Perhaps they should have gone to Death Valley to find the Manson Family hiding out, waiting for the race war to blow over.