The Conciergerie, in the heart of Paris, on the Ile de la Cité, was built in the 14th century as a royal palace. After the king left, it was ruled by the Concierge, hence the name. Not much is left of the original constructuion, but the beautiful hall of the warriors is still intact. Wonderful gothic architecture.
Later, the Conciergerie was used as a prison, especially during the revolution, when thousands of people spent their last hours here. The cell of Marie Antoinette looks reasonably comfortable, but the less you could pay, the less comfortable the cells were. Nothing to pay meant having nothing more than a bit of straw and a lot of companions… whether you liked it or not!