French Flanders is a part of the historical County of Flanders in present-day France. The region lies in the modern-day region of Hauts-de-France and roughly corresponds to the arrondissements of Lille, Douai and Dunkirk on the northern border with Belgium. Lille is the fourth largest city in France (after Paris, Marseille and Lyon), the biggest city of the Hauts-de-France region, and the capital of French Flanders (near France`s border with Belgium). Opal Coast (Cote d`Opale) is a coast in northern France, on the English Channel, popular with tourists. The Opal Coast takes its name after the stone. The opal is indeed known for its opalescence, fluorescence and iridescence that produce a unique pearly luster.