Board Thread:Lords of Shadow 2/@comment-24686422-20140330064950/@comment-84.240.34.141-20170415203609

More or less, the Castle is Inner Dracula, and Inner Dracula is a part of Gabriel's character. The Castle's not exactly "real" per se but a product of Gabriel's psyche which was brought to some semblance of life with the help of Inner's influence and the blood of all those who Gabriel killed. This would also explain why it is in a such decrepit/ruined state and how others who "do not belong" like Alucard and Marie can still visit it.

All other inhabitants are merely projections whom Inner summons to impede Gabriel's progress. In other words, Gabriel literally has a pocket plane /w the Castle bound to him and when something traumatic/meaningful happens, he "retreats" to it as a knee-jerk response to stress. And Inner is in charge of keeping this pocket dimension relatively stable because it is what it is.