As I've mentioned previously, I will watch almost any movie set in San Francisco, no matter how bad, and Beyond the Door is bad. But for almost all of its running time, it's the good kind of bad.
The plot is basically Rosemary's Baby meets The Exorcist, and it doesn't pretend to be anything more than that, right down to the weird fact that one of the kids in the movie is always drinking Campbell's pea soup straight out of the can with a straw. (He also has a poster of the can on his wall.)
Juliet Mills stars as the mother of two who finds herself pregnant with a fetus that's growing unusually fast. Also unusual? Her spinning head and green vomit, though I guess none of that would be too unusual to anyone who had seen The Exorcist a year earlier.
While the movie is categorically bad, there are some good moments. One really good scene starts out with her two kids talking about whether or not toys come alive when you aren't looking, basically predicting the plot of Toy Story, and it then turns into a really creepy moment that's totally out of Poltergeist, which wouldn't come out for another eight years.
There's also an insane scene where the husband is walking down the streets of Berkeley while being harassed by a group of street musicians, one of whom is playing a flute with his nose. This scene goes on for a long...long time.
Since it was an Italian production, all of the dialogue was dubbed in post. Star Juliet Mills handles that ask pretty well, but everyone else...does not. Particularly nutty is the pre-teen daughter's voice, which sounds like it's coming from a foul-mouthed college student.
As for the aforementioned San Francisco setting, this is one of the rare movies that is set in the City and was actually filmed in the City; lots of good footage of the Embarcadero, Ghirardelli Square, and the Cannery.
Oh, also? I don't know just what door the title is talking about, so couldn't begin to tell you what's beyond it.
I watched Beyond the Door on Shudder, and it is also streaming on YouTube.