River North

The River North area of Chicago boasts the largest commercial building in the world (square footage) at its center, the Merchandise Mart. Built in 1931 by Marshall Field and Company to replace H.H. Ricardson's Marshall Field Wholesale store, it was the building with the largest floor area in the world. That title is now held by the Pentagon in Washington, D.C., but the Merchandise Mart is still an immense office building with 13.6 km of corridors; it is still the largest commercial building in the world with 25 floors high and two city blocks long.