The old Eastern State Penitentiary in Philadelphia, long left in ruins and now a museum, was originally built as as a literal penitentiary, a prison in which inmates were subject to solitary confinement to encourage penitence. It's also modeled as a panopticon, with a central observatory and a system of mirrors that could allow the wardens to watch the inmates without them knowing if or when they were being observed.
I'd been postponing posting these pictures pending having something intelligent to say about Jeremy Bentham's Panopticon. I'm sadly so far behind on my reading for pleasure that I've decided just to post these as one of my occasional posts on American ruins, the lament of an American medievalist who doesn't have fabulous castles close at hand to visit on weekends. This one's just about as good as a castle. Click any of the images to enlarge.