Rivers that were natural highways for early Americans now offer a mix of the past and present for vacationers who want to relax and learn about history. Industry insiders say river cruises offer some of the best amenities of the ocean cruises but with more intimacy. The River Explorer, which is two barges joined together and pushed by a towboat, travels up and down rivers such as the Ohio, Mississippi and Missouri. Vacationers looking for more elegance can climb abroad The American Queen, billed as the largest steamboat in the world. The smaller Delta Queen offers Tiffany-style stained-glass windows and a grand staircase. Shore excursions for river travelers might include New Orleans' romantic French Quarter or the rollicking Grand Ole Opry in Nashville, Tenn.