Possible Clues:

• Cross, character climbing something on stage, perhaps
• Theatrical opening?
• Way through a floor
• Potential rowing disaster reportedly, from which Redgrave maybe escaped?
• Magician's exit
• Opening in the theater, maybe
• Vampire in corner -- cross raised
• Hatch cross-section towards the left
• Opening set in a stage or ceiling
• Cross section pulled back to reveal hidden entrance