The largest medieval city in Germany and a UNESCO World Heritage site since 2006, Regensburg was founded in 179 A.D. by the Romans. It eventually became the second-richest city in the Holy Roman Empire, prized for its trade of "White Gold," otherwise known as salt. It was even once the capital of Germany until it was moved to Munich. Be sure to include Regensburg if you're building a cruise itinerary to tour Germany.
Fortunately, most of the city was spared destruction during World War II. With Romanesque and Gothic structures, courtyards, squares and a stone bridge, the city of roughly 150,000 residents makes you feel as if you're stepping straight into a storybook setting.