Terrain feature found everywhere across the world. Unlike other features, it doesn't occupy a separate terrain tile, but extends between several tiles. A river usually starts next to a mountain tile, and it always ends in a larger water tile, such as a lake or ocean. A river will also turn adjacent flat desert tiles into flood plains, adjacent snow tiles to tundra tiles, and adjacent tundra tiles to plains. Some buildings are only available when the city is built next to a river (or a lake). They are: