Really to get into the castle you have to be on a quest or teleport to a friend in the battle with lord Nightshade
beat lord nightshade foulgaze
he is a boss of the haunted cave on the tower
fight lord nightshade
Get a banshee from lord nightshade
the end of the haunted cave
he is at the end of the hanted cave down by the tower
Well, once you reach a certain point in the game, Professor Ambrose will call you and give you a quest to defeat Foulgaze. After that you battle Lord Nightshade.
you have to be lvl. 12
he is in the tower in the hunted cave he is Lord Nightshade
by fighting lord nightshade 2 times
its really easy. get the quest to deafeat lord nightshade in stormdrain tower in haunted cave. after you deafeat him, you will get a skull key.then you can go to the nightside, but lord night shade is pretty tough... so good luck!
Beat Lord Nightshade or ask a friend who can go to Nightside to go in there. Then teleport to him or her.