So I'm a bit hesitant to post this after I got mildly ridiculed after a post about possible Cabal experiments involving cryptids and other mysterious creature sightings throughout the world, but this just makes WAY too much sense to not share.
So my theory revolves around the Book of Enoch in the Dead Sea Scrolls. For those who don't know what that is, it's a lost book of the Bible that got Tossed when Biblical canon was being standardized. The weird thing about it is, the Book of Enoch was EXTREMLY popular with early Christians and even Hebrews up until that point in time. So it makes little sense to toss it, especially since the modern Bible still has references to it, thus showing just how important it was to understanding everything in the Bible.
Anyway, history lesson aside, the Book of Enoch tells us about The Watchers, Fallen Angels different from the angels that fell with lucifer that came to Earth in the Time of Enoch, the Hebrew patriarch in the Line of Adam and Eve and ancestor of Noah. These Watchers are responsible for corrupting humanity to the point that God sent the flood to wipe the slate clean. Specifically, they taught humans knowledge that God had decided they either weren't ready for or should never know. Mostly things involving sex/sexual attraction (think alphabet crew type crap), warfare, certain types of advanced technology, etc.
Some people point to the seemingly impossible jump in advancement from hunter/gatherers to an agricultural revolution over a few thousand years as proof of the watchers existence. There's actually MANY different ancient cultural representations of similar beings in nearly every ancient culture. The oldest being the Annunaki of ancient Sumer (think like Gilgamesh.)
Regardless of how old they are exactly, the watchers are responsible for the existence of Giants known as Nephilim, angel/human cannibalistic giants resulting from the watcher raping human women. All of this combined, the giant abominations, the rampant sin, the unholy knowledge, etc. all eventually led to Noah and the flood.
But before the flood, God killed all of the Nephilim, and punished all of the Watchers by imprisoning them under the Earth until the end of time where they'll be punished alongside the devil at the final judgement.
NOW THEN. With the backstory out the way, here's my theory.
EVERYTHING going on is a result of the watchers. At some point in time, probably 1500 years ago or a little longer, someone found a cave, that led into a tunnel system. This cave system was a "DUMB" created by God that led FAR below the Earth to imprison the Watchers. When this random person found the cave and explored it, they eventually found one of them.
Then the Watcher began manipulating this poor soul into being their pawn. Thus the cabal was born. Over the next 1000+ years the Watchers would use their new human pawns to build the cabal, create and hide secret advanced technology, advance their perverse sexually abhorrent agenda, corrupt as many people as possible, demand human sacrifices, etc.
THAT is what's under the vatican. It's a direct tunnel to a watcher prison. The watchers told them about adrenochrome. The watchers have been providing them with more and more advanced technology that they then hide from the masses so they can benefit themselves while treating us as slaves.
This is why Q said it's going to be Biblical. The Book of Enoch IS real, and when all of this is done, we're going to have proof of fallen angels existing. And if they exist, EVERYTHING in the Bible exists. I realize this isn't an all encompassing theory and there may be a few holes, but I'm trying to get everything down and out of my mind before I forget it.
perhaps the rapture already happened. its certainly possible that the 'dark ages' are the suppressed history of Christ's 1000yr reign on earth. God took all the true Christians up already - left the athiests and jews and lukewarm christians here - and we inherited their cathedrals and cities and essentially live in the rubble of their civilization. kind of a crappy take on it but also worth looking into. check out Exploring Tartaria on yt its got some good content and brings up good points to consider for the OP because it does reference the nephilim etc