One of my players just sent this to me - an article about Houska Castle, near Prague in the Czech Republic. It reminded him of Felltower.
"Supposedly, a gate to hell opened on the craggy Czech mountain. The castle was constructed around the portal, and a chapel was plopped directly atop the hole to keep evil monsters from spilling out of the underworld and slipping into the human realm.
Folklore says the supposed gate to hell was so deep no one could see the bottom of it, and those who did attempt to enter the dark orifice encountered demonic human-animal hybrids."
That sure would explain some of the enduring mysteries about Felltower . . . and confirm those rumors that there is either a gate to Hell in its depths or the dungeons keep on going down until you reach Hell itself. Neither would be implausible, and the various placed sanctified to the Good God in its depths are likely part of attempts to seal or limit the penetration of evil into the world.
I'm not saying it is, but it could be, and might be. The players will have to find out.
It was even occupied by Nazis and used as an administrative center. Felltower was occupied by more than one group with malign political ambitions and unsavory and evil practices. And it was the administrative center of Sterick's brief dominion of the northern reaches.
So this fits in so many ways, potentially.
Plus, as I finish up Darklands, I wonder if my final battle with evil will take place near Prague? If this article is correct, I very well may.