A brass letterbox in the lobby of the Frick Building downtown. Letters come down the shaft from the upper floors and into this miniature postal temple, where they are treated royally for a few hours until they have to be transferred to a humble mailbag.
UPDATE: Note the clarification from the kind commenter below, who points out that the shaft is no longer in use. What would H. C. Frick say if you told him he had to walk all the way down to the lobby to deposit his outgoing mail? (It’s a trick question: H. C. Frick would of course reply, “No, you have to walk all the way down to the lobby to deposit my outgoing mail.”)