from the article in The Chronicle --
"Yet all of these attempts at explanation share the assumption that the etchings are not about architecture so much as they are about what Victor Hugo called "Piranesi's dark brain." The etchings are both "Imaginary Prisons" and "Prisons of the Imagination"—the prison as the inside of the skull. That is perhaps the most modern thing about them: They anticipate the belief that any subject is an excuse for illustrating the artist's mental state, that every portrait has a self-portrait underneath. In these etchings, Piranesi invented architecture as metaphor for the mind."