Possibly not the one you’re thinking of: the 1969 television short directed (and partly written) by Jim Henson. You can find it on YouTube here. People don’t always realize that in addition to his other roles, Henson was also an experimental film maker. Very experimental.
I really have no idea what “The Cube” was supposed to mean, if anything. I tend to dislike self-consciously trippy attempts to expand people’s minds, and there’s a lot to dislike here. Especially as the main character doesn’t really seem to respond as we expect a normal person would in equivalent situations. But I also enjoy puzzles and trying to find meaning in tantalizingly ambiguous messages.
Quite a lot of the movie can be considered a sort of riddle; if you suspend your initial, straightforward interpretation of events and look aslant, interesting alternatives appear. One thought that occurs to me is… let’s put it in ROT13 just to avoid casual spoilers… gung gur frrzvatyl zbpxvat gnhag “lbh’yy arire trg bhg ‘gvy lbh’er qrnq” pna unir zber guna bar vagrecergngvba. Yvsr vf n fgngr gung lbh pna’g trg bhg bs jvgubhg qlvat, vfa’g vg?
Occluded Sun 