The view from the old city wall is beautiful and you can easily spent some time hanging around there. When you get up early and go to the city wall the city looks beautiful in the foggy morning light. Visit the Casemates (the fortified wall) where you can actually walk inside the wall since it used to be a castle.
Downtown, the Place d'Armes and the Place Guillaume are interesting and a place where lots of people gather. The city is beautiful, with nice little streets and squares, beautiful buildings and parks. It really shows the people have a lot of money, you hardly see any small cars and I didn't see any homeless people at all.