The Keep. 1983.
During WWII German soldiers occupy a part of Romania and make a fortress their base and dismiss the warnings about it and something is released that kills them.
Jurgen Prochnow plays another German soldier (last he played a German Captain in Das Boot) leads his platoon to The Keep and is informed by Caretaker W. Morgan Sheppard to not stay there and ignore the dire warnings. Gabriel Byrne plays the Major who wants to understand what the writing means and brings in Sir Ian McKellen who wants to stop the invasions. Scott Glenn plays the somewhat traveller who wants The Keep closed and the entity to stay where it is or destroy it.
One film that was made on a good budget but apparently it flopped, yet even today it's a classic, I gotta say why isn't this in the 1001 movies you must see before you die list?? It has everything a great movie should have, a dark mysterious plot, good actors that provide everything their characters need to be, tough, ruthless, empathy, and a great demon/monster. Perfect direction from Michael Mann who went on to create other great films and a haunting background score by Tangerine Dream that blends in well with the film.
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Will we ever see the full 3 hours version of this???