Just outside downtown Pittsburgh
"Steel City" isn't just a random nickname for Pittsburgh. It is based on their steel producing past and how many families, including the Carnegies, became rich because of the steel factories that were prevalent in the area during the 1800s.
One of the last remaining pre World War II blast furnaces still stands in Pittsburgh. The Rivers of Steel: Carrie Blast Furnaces National Historic Landmark has tours that show the beginnings of the industry until the time the furnace closed in 1982. There is still some metal bits scattered around the premises and the ruins are now canvases for street art.