Merchandise Mart

At that time, when it was constructed 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 was taken in 1941 by the Pentagon in Washington, DC, 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.

The complex was renovated between 1986 and 1991 and now contains a shopping mall on the first two floors. The rest of the building contains showrooms where design professionals choose home and office furnishings.

Guided tours of the Merchandise Mart are available; for info see their website.