As a tourist destination for the Midwest, Duluth has America's only all-freshwater aquarium, the Great Lakes Aquarium. Duluth is known for the Aerial Lift Bridge, which spans the Duluth Ship Canal into the Duluth-Superior Harbor. People also visit Minnesota Point (known as Park Point locally), one of the world's longest freshwater sand spits, that is long. People come to the city to start vehicle trips along Minnesota's famous North Shore. Each year, 16,000 people come to Duluth to run the "Grandma's Marathon". The 610' long William A Irvin is a museum ship that used to be the flagship of the United States Steel ore carrier fleet.