Venice is world-famous for its canals. It is built on an archipelago of 118 islands formed by 177 canals in a shallow lagoon. The islands on which the city is built are connected by about 400 bridges. In the old center, the canals serve the function of roads, and every form of transport is on water or on foot. In the 19th century a causeway to the mainland brought a railway station to Venice, and an automobile causeway and parking lot was added in the 20th century. Beyond these land entrances at the northern edge of the city, transportation within the city remains, as it was in centuries past, entirely on water or on foot. Venice is Europe's largest urban car free area, unique in Europe in remaining a sizable functioning city in the 21st century entirely without motorcars or trucks.