The Gateway Arch
Credit: Agnieszka Szymczak / Getty Images

Eero Saarinen's arch was controversial when it was first constructed. Not only was it modern – designed in part to be seen from the newly constructed interstates weaving around St. Louis – it towered over center city, casting some of the largest buildings in shadow. But the controversy died down and the structure became a calling card for both St. Louis and Saarinen, who went on to design John Deere's Illinois headquartersNew York's TWA Terminal, and about half the furniture you see on Mad Men. Though it failed to revitalize the city, the building attracts roughly three million visitors annually, making it one of the Midwest's most popular destinations.