key to the midway

Etymology
slang, from the custom of sending a rube on a quest for the (non-existent) “key to the midway”.

Noun

 * 1) A fictional item, the subject of a fool's errand.
 * 2) A Ferris wheel or carousel, due to their central location.
 * 3) * 1985, Rob Karwath, “The Gritty Side Of Life Along The Midway”, Chicago Tribune, August 14, 1985:
 * "en"

- “I’m a wheel man,” he says. “I’ve been crazy about Ferris wheels since I was a kid. The Ferris wheel is the key to the midway. When it’s up and running and the lights are on, everybody knows the show is open.”