I personally though DoS's castle Walter's Castle(LoI), just renovated over the centuries and modernized by the cult. All the areas of Walter's Castle are accounted for(Garden, Waterfall, Theater-like area, Chapel, Alchemy Lab, Keep), as well as the Prison of Eternal Torture, which I can see the Condemned Tower and Mines of Judgement being built on. Other newer areas were built centuries later. I mean, if you take it that LoI happened in 1094 and we never return to it. Within that time(between LoI and DoS), a LOT of things could've happened, different nobles could've reconstructed the castle, towns were built around it, and it's dark history summoned those with evil intention. It lacks the great power of Dracula's Castle, but I could still see it being a sacred "unholy place" to Dracula sympathists(it basically was where Mathias became Dracula, after all). Symbolism and all, especially for Dark Lord candidates.
That's just me, though.