Tumbling down from the Appalachians, both of these rivers take their time reaching the Mississippi, meandering routes through the American heartland and some of the nation's most interesting cities. Many of the cruises along these waterways have specific themes — in particular bourbon, music, and the Civil War — but nearly all voyages cover a bit of all three. There's also a choice of old-time paddle wheelers or modern ships, and departures either in the summer or (in a limited capacity) in the fall.