Beneath the Planet of the Apes

Skippable, and the strangest decision in the series is buried in it. Heston did not want to return and agreed only on the condition that his character be killed, and then went further: he reportedly pushed for an ending that would make sequels impossible. The film duly ends with the destruction of the entire planet, and the series continued anyway by sending three characters back in time before it happened.

The first half is a straightforward repeat with a new astronaut who looks and behaves almost exactly like the previous one, which the film never acknowledges. The second half goes somewhere else entirely. Beneath the ruins of New York there is a colony of telepathic mutants who wear human masks over scarred faces and conduct religious services around an unexploded cobalt bomb, singing hymns to it.

That is a genuinely bizarre image and it is the only reason to watch this. The budget was cut sharply after the first film, so the ape city is reused, the crowd scenes are thin, and the fighting at the end is badly staged. The telepathy is conveyed by actors clutching their heads.

Nothing in the rest of the series depends on it except the ending, which Escape refers to without requiring you to have watched this. Skip it on a first pass and lose nothing but the masks.