The Keep (1983)

They were all drawn to the keep. Tonight, they will all face the evil.

Set during World War II, a German army garrison is sent to guard a mountain pass in a village in Romania's Carpathian mountains and sets up barracks in an ancient stone fortress. Two of the soldiers unwittingly release a mysterious entity that kills or corrupts those within its influence, drawing the attention of a Gestapo commander, a Jewish scholar, and a mysterious traveller.