Perhaps the most (if not the only) interesting city in West Africa. The first European colony in this part of the mainland, named after King Louis XIV. The historical part of the city is located on an island 2 km long and 400 meters wide.
Quote from the UNESCO website: "Founded in the 17th century as a French colonial settlement, Saint-Louis became a city in the middle of the 19th century. It was the capital of Senegal from 1872-1957 and played an important cultural and economic role for all of West Africa. Location of the city on an island at the mouth of the Senegal River, its regular layout, embankment system and characteristic colonial architecture give the appearance of Saint-Louis integrity and unique features."