Image from YouTube
A 1981 St. Joseph News-Press article said the exhibit "splits vision with a vertical mirror."
The exhibit is long gone. The image above is from a Texas Sesame Place commercial, but most of the footage was clearly shot in Langhorne.
I assume the commercial was shot before the Texas park was finished and the Cheshire Cat featured was in Pennsylvania.
The name Cheshire Cat refers to the character from Alice's Adventures in Wonderland who could appear and disappear at will.
Incidentally, Cookie Monster played "The Cheshire Cookie Cat" in a 2008 Sesame Street DVD:
Image from MuppetWiki