that fascinates people? It isn't too hard to work it out. Everything that exists is in some degree a symbol, a message, a word. It speaks of something else. Poetry brings out and capitalizes upon that eloquence of things, that magical web of analogy. Jacques Maritain's book Creative Intuition in Art and Poetry is all about that. A doorway is a particularly potent symbol, because it represents the transition between two places, or two states of being. (I find it surprising there is not more about doors in Rene Guenon's Symbols of Sacred Science.)
Illustrations show the old door to the School of Metaphysics at the Bodleian Library, and the Romanesque entrance to St Mary's Church in Iffley, near Oxford. For more doors see here.