Jim Henson’s The Cube (1969). An episode of NBC Experiment in Television (53 minutes). Starring Richard Schaal. Reminds me a bit of Head.
Bet you haven’t seen this!
Prescient as all get out. Like Shock Treatment, it (among other things) predicts reality TV.
Also some very good WTF is going on here, played both for laughs and for wonder and creep, and I thoroughly enjoy it.
"Your trouble is, you will not accept a paradox."
Parts of it are positively Lynchian. Or maybe a prank pulled by Guy Grand.