"The Stage"

 The Auditorium is a room.
"A vast area with a stage, main floor, and a balcony.".

an enterable supporter called a stage is in the Auditorium.
the description is "This spacious stage can hold upwards of 1000 actors!".

the stage is scenery.

lying on is an action applying to one thing.
understand "lie on[something]" as lying on.

instead of lying on the stage when the player is on the stage:
say "But you're already on the stage.".

instead of lying on the stage:
say "You lie on the stage.";
move the player to the stage;
stop the action.

after searching the stage:
move the props to the stage;
say "you discover a bunch of fancy props.".
	
instead of taking the props, say
 "A disembodied voice yells out 'Leave [apostrophe]em alone!'".

the props is a thing.
the description is " a bunch of fancy stage props.".