What is the importance of the castle in the novel, Fairest of All: A Tale of the Wicked Queen?

The Castle is where the King and Queen are married, and where the Queen rules over the land after her husband dies. The castle is a massive, cavernous building once filled with warmth and love of a beautiful new family. After the King dies and Queen descends into madness, the castle's description changes into a cold, hollow cave, reflecting the love lost.