Although this is the family of the shameful attempted villainess in the original story... These hidden facts about her family's background are so dope it's a waste they didn't appear in the novel.
I mean... Now that I think about it, the novel was told from the female lead' point of view... So I guess it's comprehensible she didn't know much of these kinds of things given that they seem to be family secrets and she was obviously on bad terms with the failed Villain Theressa is. However... In the novel things of mysterious provenance like the archaic sword and this door never appeared nor were mentioned in front of her.
If these types of objects had been added to it, it would have given the novel a great spice. Therefore, I can't believe the creator of this fictional world didn't even imply the existence of such mystic objects.