LILLE , by far the largest city in the north, is the very symbol of French industry and working-class politics. Its mayor, Pierre Mauroy, was the first Socialist prime minister appointed by Mitterrand in 1981. The city has a lovely centre, Vieux Lille, some vibrant and obviously prosperous commercial areas, modern residential squares, a large university, a brand-new métro system, and a very serious attitude to its culture and restaurants. Although you may not consider Lille a prime destination, if you're travelling through this region it's worth at least a day and a night.