Louis Kahn is considered one of 20th century's most important and influential architects. His unique buildings span the world from California to Bangladesh. But it is the one building he DIDN'T build that might be the most influential of them all.

Kahn, who was born in Estonia, spent a large portion of his life in Philadelphia. Much of his work was centered around the area. Now, apologies to those who love Philly, but we'll come out and say it: it's a dump. Kahn wanted to revitalize it through architecture, proposing a new city hall: the City Tower. This.

Grotesque? Revolutionary? Absurd? Futuristic? Ridiculous? Fantastic? Whatever the case is, the City Tower never came to fruition. However, it is considered a visionary design that influenced numerous other architects.

And, come on, have you been to downtown Philly? Say what you want about the City Tower, at least it would have made it interesting...