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As is the case with all Luis Buñuel films (The Experimenting Angel and Belle de Jour come to mind), Viridiana is a difficult movie to categorise or even fully explain.

On the surface, it's the story of the titular character (Silvia Pinal), a nun who accepts an invitation to visit her widower uncle (Fernando Rey), who's grief over his wife's death leads him to become dangerously obsessed with his fearful niece.

What follows is a deeply troubling surrealist nightmare, which under its core story works as a bleak look into the life of a woman confused by the misfortunes of the world and eventually desperate to reconcile some of the pain that surrounds her.

Viridiana was deemed blasphemous when it came out, reviled by the Vatican and noted for its religious symbolism, but all told it's a story about the difficulties of change and the complexities of guilt. Not an easy film to digest by any stretch, but one everyone should see and attempt to understand on their own terms.