As per your request earlier, I specifically tried to fill in some info on the Charnites, none of which contradicted what you said. Some nice guy can make a castle, the next owner might be a murderous SOB, and the next owner might seal off the torture chamber after beheading the guy and taking it himself. Centuries later, as is the case in the real world, locals can live near a ruin and ever hang out around it, blissfully unaware of some hidden chamber until some archeologist digs it up, usually after their told him how they knew every inch of the place and chuckled at his wasting time trying to find stuff.

Other than quickly mentioning that the evil old empire had an architectural taste for catacombs - and it's worth noting that there's no reason why someone from there might discontinue the practice, germans who didn't like the Nazi's didn't remodel their houses to non-german styles - all I did was explain about some evil creature that might be dangerous, suggest they should avoid it, then ask them if they might know of some hidden place. I couldn't really add to their story, I don't know where your aiming for with it, and my own character is unlikely to know about that. Keep in mind, we can only know about them what you specifically write, you may think you're giving us very specific details without realizing that there's a lot vagueness about them.