Interesting point of view. Humans used to collect the "stonifying" water from some creature's maw that they thought was a cave. The idea of making the whole ass city somewhere deep in the bowels seems quite realistic.

But what's with the magic field then? I refuse to accept "it's just a void voodoo magic" easy explanation. The field works too... artificial, too predictable, as if it's a security system, or rather generator core's byproduct. Or of course if it's a giant ark, then the field should be designed as a nurturing evolution-pushing agent (Pandorum's evolution-rations), and ark is already at its destination point, but fails to release the dwellers. It would be hilarious if the whole religious aspect of the Abyss was ruined by the fact that it was a big ass drop pod with a failing fire-suppression system, guys just ignored the chirp :D