Directed by Michael Mann, panned by nearly everyone (including the author of the original novel, F. Paul Wilson), The Keep remains one of those strange fascinations for me. I suppose the greatest attraction is probably lamenting something that could have been and not what actually was.
The plot, for those who care, from Wikipedia:
The film focuses on a deserted citadel (the “Keep” of the title) in WWII Romania within which lies entrapped a dangerous and malevolent entity named Radu Molasar. When the German Wehrmacht occupies the castle to control the Dinu Mountain Pass, Molasar is unwittingly unleashed from deep within the innermost recesses of the citadel by a pair of treasure-seeking soldiers and he consumes their life energy. A detachment of Einsatzkommandos then arrives to deal with what is thought to be partisan activity. The Einsatzkommandos' actions only fuel the demon's hunger for bloodshed and soon more troops begin to die in mysterious, gruesome ways.
At the instigation of the local priest, the Germans retrieve a Jewish historian, Professor Cuza, from a death camp to decipher a mysterious message emblazoned on a wall of the keep. The demonic and, at this point, cloudlike Molasar saves the professor's daughter, Eva Cuza, from a sexual assault by two Einsatzkommandos and then enlists the aid of her grateful father to escape from the Keep. Cuza is also cured of his debilitating scleroderma by the touch of Molasar and therefore becomes doubly indebted to the malevolent entity. A mysterious stranger arrives to foil this plan, however. After a misguided and unsuccessful attempt by the professor to have the stranger stopped, the two supernatural beings engage in a confrontation in which the demon is weakened and drawn back into the innermost recesses, and the hero inevitably finds himself pulled in as well, his fate linked with the demon that was his destined foe to guard from ever escaping the Keep.