The Château d'If is a fortress on an island in the bay of Marseille. It was used as a prison in the 18th and 19th Centuries. It's most famous prisoner was the (fictional) Count of Monte Cristo in the eponymous tale by Alexandre Dumas. This light show was in one of the cells.
The film The Count of Monte Cristo has just been shown at Cannes and may be coming to a cinema near you this summer
