Ante Room II is the starting place for the Return to Dark Castle new levels. Each time you come to this room you get all your lives back, and your game is automatically saved. There are seven exits to this room. The center one is closed when the game starts. There are also 10 pedastals for the Orbs you collect. When all ten are filled, then the Skull Door will open and you can do the Dark Knight Path.
See List of Levels in Return to Dark Castle for info on where each of the doors leads.