Two of my favourite films ever made are 12 Monkeys and Pan's Labyrinth. After thinking about the nature of storytelling for awhile, I've come to the conclusion that part of the reason I derive so much enjoyment from these films is because in each case, there are at least two valid ways of interpreting the film - all the sci-fi/fantasy plot elements were just hallucinations occurring in the main character's head, or everything depicted in the film really happened. Similarly, V for Vendetta (both the comic and, to a lesser extent, the film, though the comic was better) leaves open for discussion the question whether the title character is mad or rational, benevolent or a menace. I'm looking forward to viewing David Lynch's Mulholland Dr. because I'm told it has the same open-ended structure as the above-listed works; I'm growing convinced that great art shouldn't supply audiences with all the answers, and that it's more important for it to ask provocative questions. Are there any other films (or, for that matter, works in any other medium) that you consider to be similarly open-ended? I'm curious to read about what people have enjoyed.