The focal point of the citadel in Sisteron is the chapel sat just below the upper ramparts. Unfortunately, it was bombed in the second World War and has had to be completely restored.
To the left of the chapel you can see a tower which is actually built on the top of the bridge. On the front you can see a very small window. This marks the room Prince Jean Casimir Vasa, future king of Poland, was held captive for a whole year. The winter spent up there must have been brutal.