What a lovely website - their photos of "hidden Paris" are amazing - Paris Photography Walking Tour. Site has GPS locations for every photo on the tour so you can find them yourself for free!
Spiral staircase at La Conciergerie, Paris. Former royal palace and prison in on the Île de la Cité, it is part of the larger complex known as the Palais de Justice. Built in the Middle Ages as a Merovingian Palace.