The Third Man is one of those films which is like a Looking Glass Door into a dream reality. There's the film itself, with its characters and ideas, high quality stuff throughout. But also there is this idea of a whole city there, post-war Vienna. You feel it's tantalisingly close, and you could slip through into it, and have a doomed love affair and drink coffee and run about those black and white streets.
Those are the cult films and TV shows, the ones that seem to be a small window onto something much bigger hiding out of sight, like the parts of the parlour that Alice couldn't see in the mirror.