The building has two distinct sides: a proud and austere - and magnificently restored - 14C keep, with crenellated walls and machicolations still intact, and a majestic 17C section with a royal courtyard and chapel which boasts fine stained-glass windows dating from the Renaissance. The keep is the only medieval royal residence to have survived in France. It was used as a State prison in the 16C, mainly for political prisoners, including characters such as the Grand Condé, the Cardinal de Retz, Diderot and the Marquis de Sade.