Let's cut straight to the chase here.  The Space Center is home to many cool things, but what makes it important is that it is home to the single most beautiful building in the Western Hemisphere (quite possibly even the world): the Vehicle Assembly Building.

The VAB is so big it creates its own weather inside.  Each of those grey things running up the side is a door that weighs thirteen tons.  OK, so I'm making this up.  But I think the VAB speaks for itself.

As an architectural innovation the VAB has had wide-reaching impact on American society.  In this photo we can see that even portable toilets are designed to echo the powerful austerity of that blankly heroic, yet somehow protean, exterior.