Merchandise Mart is one of the most massive buildings in the world, and when it opened in 1930, it was. Clocking in at 4,000,000 square feet, this River North Titanic was originally owned by the Marshall Field family (sound familiar?), and it served as a central mother ship of wholesale goods businesses. The Mart is an incredible feat in art deco construction, nestled right alongside the Chicago River. At night, the building's upper floors are splashed with colored lights, making it stand out as a vibrant beacon downtown. The Mart remains a massive hub for retail and wholesale, with plenty of spots for customers to visit.