By Plane. The Louisville airport, Standiford Field (SDF), is served by all major airlines. It is not a hub, not for people anyway (see below), so you may have to change planes.
Background. Louisville is the international hub for United Parcel Service (UPS). Starting around midnight, a legion of 747s and other "brown tails" land in Louisville and unload a million or so packages. The automated sorting operation stretches as far as the eye can see, with minimal human intervention, and is an impressive sight. Around 4am, the planes load up and take off to destinations around the world.
By Car. Louisville is located in Kentucky on the Ohio river, at the intersection of I-64, I-65, and I-71. St. Louis is to the west, Indianapolis is to the north, Cincinnati is to the east, and Nashville is to the south.