Here is an interesting and mind-screwing film called "The Cube" directed and produced by Jim Henson prior to his focus on the Muppets. The film stars Robert Schaal as "The man in the cube".
From the Google video description:
This philosophical teleplay covers many themes such as, the nature of reality, individual versus scientific perception, self-reference, man's relation to others and society, insanity, social projections, and race relations. It originally aired on NBC's weekly anthology television show NBC Experiment in Television February 23, 1969. The production was produced and directed by Jim Henson, and was one of several experiments with the live-action film medium which he conducted in the 1960s, before focusing entirely on the Muppets and other puppet works. The screenplay was co-written by long-time Muppet writer Jerry Juhl (who also appears in a cameo).
[via meshly]