Burnham and Root, Louis Sullivan, Frank Lloyd Wright and Ludwig Mies van der Rohe all created groundbreaking buildings in Chicago. And the world’s first skyscraper, the elegant terra-cotta and plate-glass Reliance Building, still stands at 1 West Washington Street. In addition to walking tours, the Chicago Architecture Foundation conducts tours by bus, “L” train, bike and even Segway. But my favorite is the River Cruise.