In Lyon, the most magical time of year is the 4 day long Fête des Lumières. This Fête celebrates French media artists. Using lasers and projections their videos and graphic media is projected onto different Lyonnaise buildings including churches, government buildings and even the ancient Roman amphitheatre. Using lights of all kinds, the city it lit to a T. At each building, there is a different show and you have 4 nights to see all the shows.
Cathedral in Vieux Lyon
Hôtel de Ville
I truly have no words to describe this experience. Despite the cold and the rain (I am still chilly just thinking about it) it was one of the most magical things I have seen while in Europe.
If you ever get a chance to go to Lyon, especially during Fête des Lumières, I would highly recommend it.