Spend a leisurely day onboard as you cruise along a marvel of modern engineering, the 106-mile-long Main-Danube Canal. Tonight, celebrate Christmas Eve in the enchanting town of Regensburg. For more than 1,200 years, European leaders dreamed of linking the great rivers of Central Europe: the Rhine, Main and Danube. And in 1992, an engineering masterpiece, the 106-mile (170-kilometer) long Main-Danube Canal, made this dream come true. This masterwork allows ships of all shapes and sizes to readily transit from the Rhine Delta in the Netherlands to the Danube Delta in Romania, connecting the North Sea to the Black Sea. The canal crosses the European Divide at 1,331 feet (405 meters) above sea level, climbing the summit by way of a series of impressive locks; the highest will lift your boat about 83 feet (25 meters). The canal then follows the natural course of the Altmühl Valley, a picturesque area of limestone mountains and Franconian villages, before it joins the Danube near Regensburg. Don’t miss the fascinating process as your ship navigates the locks—or the wonderful scenery on either side of them. You’ll arrive in Regensburg this evening, with the town celebrating Christmas Eve. You’ll be free to explore the UNESCO-designated medieval city on your own, and if you like, you may attend midnight Mass in one of Regensburg’s historic churches.