Possible Clues:

• Secret exit, perhaps
• Means of access set in floor or ceiling
• Hinged exit in floor or ceiling
• Reversed cross section opening between floors
•     Magician's secret exit
• Means of entry through floor or ceiling
• Cross-piece replaced in opening
• When upset, cross to leave by stage exit
• Door set in a stage
• It ensures that pantomime characters go down well