In this photo you see the beautiful Church of Saint Nicolas and the traditional street market bellow the Castle. The Church of Saint Nicolas was built in the XII century. The interior of this church, inspired by the Chartres Cathedral, is quite interesting.
In Blois there is another church you should visit, the Cathedral of Saint Louis. This Cathedral sits close to the Town Hall (=Hotel de la Ville). The Cathedral is a late Gothic Church built in the XVII century over the rest of an old Carolingian crypt.