The Ninth Configuration (movie, 1980)

Col. Vincent Kane is a military psychiatrist who takes charge of an army mental hospital situated in a secluded castle. Among Kane's many eccentric patients is Capt. Billy Cutshaw, a troubled astronaut in the midst of an existential crisis. Although Kane's own grasp on sanity is questionable, he manages to engage Cutshaw in a series of thoughtful conversations about science and faith that deeply affect the lives of both men.