The Boardwalk

Looking at the shops and crowds of Navy Pier today, it may be hard to imagine that Chicago's number one tourist attraction was built in part to revive the city's dwindling downtown shipping industry. The original pier, built in 1916, was filled with commercial warehouses and lined with docks for lake freighters to load and unload cargo. The 3,000-foot pier proved to be no match, though, for the bustling harbors of South Chicago and Milwaukee.

Navy Pier is a good place to get an up-close view of the man-made shoreline that stretches across most of the city's border with Lake Michigan.The two sea walls just south of the pier – one lined with metal, the other with rocks – serve as a kind of armor for the shoreline, protecting it from erosion and flooding. Both types of sea walls reduce the brunt of incoming waves, but the rocks can also double as habitat for fish, invertebrates, and even bacteria that prefer rocky shores.