Made for the “NBC Experiment in Television” series in 1969. A man finds himself stuck in a plain white cube. Very absurdist/existentialist, with occasional metatextual touches. No causal relation as far as I know with the later sci-fi horror series Cube. Written by Henson with Jerry Juhl and starring Jerry Nelson. Does not include any puppets.
. . . I won’t claim that it’s a great movie, but it is a curiosity, and a charmingly kooky product of its time.