Headcanon: Any good people, animals, etc. engulfed and destroyed by the walls of the castle become lost souls, which inhabit the torches and candles of the castle.
On that note - the Merchant in Harmony of Dissonance mentions that he was caught up in a dense fog on his travels and 'ended up' in Dracula's Castle. If we take that at face value, it seems that the Castle materialized around him and he found himself trapped inside it... although he was able to 'set up shop' and didn't become a lost soul/candle.
Edit: Whoops, accidental double post.