The scariest movie I saw as a child was:

[Angrboda]

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Caution: Spoilers:

The storyline, which is largely faithful to the original television production, centres on the discovery of a mysterious object buried at the site of an extension to the London Underground. Also uncovered nearby are the remains of early human ancestors more than five million years old. Realising that the object is in fact an ancient Martian spacecraft, Quatermass deduces that the aliens have influenced human evolution and the development of human intelligence. The spacecraft has an intelligence of its own, and once uncovered begins to exert a malign influence, resurrecting Martian memories and instincts buried deep within the human psyche.

https://en.wikipedia.org/wiki/Quatermass...Pit_(film)

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