The castle was cursed thousands of years ago by a mother who sacrificed her son for her people. She was the queen of the Vampires and was married to the vampire king but she had relations with the king of the demons, the devil. She got pregnant with the devil's child and bore a beast, a Vampire-Demon. Half Vampire, half demon. he was uncontrollable and just had to be locked up least he wiped out their race. she locked herself in the castle with her son and cursed the castle - whatever came into it would never go out except the beast was killed, which was nearly impossible as no one could ever touch the beast.