This fortress like building on the Ile-de-la-Cité, built by Philippe the Fair (1284-1314) now makes up much of the Palais de Justice complex. Its history as a place of imprisonment, torture, and death is is significant. That said, it does have some beautiful features, in particular the Salle des Gardes - the room of the guards with elegant vaulting - the colonnaded Salle des Gens d'Armes - 69m long and 27m wide now sometimes used for concerts - and the Cuisines with its four large fireplaces, each large enough to roast an entire ox.
Among its more famous prisoners were Marie Antoinette, Charlotte Corday, Danton, and Chenie. Marie Antoinette's cell is now a chapel to her memory, and includes her crucifix, and two portraits of her from life. (paris pages.org)