This an existential psychological play was named "The Man in the Cube"
and was written and produced by Jim Hensen (prior to his Muppets
productions). It was broadcast on NBC's "Experiments in Television"
series in 1969. It stars actor Richard Schaal, father of actress Wendy
Schaal and one-time husband of Valerie Harper.This kind of explains why Sesame Street is so dark in places.
It very much like the Twilight Zone epsiode were the people are in the
create and trying to get out, only to find they are toys in a toy box.
Also like the film The Cube