While in Regensburg, cross the impressive 12th century Stone Bridge spanning the Danube that has stood the test of time in Regensburg's medieval old town, a UNESCO World Heritage site frozen in the Middle Ages. As you wander Regensburg's winding streets, don't miss the magnificent Gothic cathedral with its colorful stained glass windows and the historic Wurstkuchl, one of Germany's oldest restaurants serving traditional sausages since the 12th century. Then head to Ingolstadt to see the imposing New Castle with its distinctive circular towers and the Audi Museum, which shows off the brand's century-long automotive history. In Ingolstadt, you can also visit the Anatomical Institute, which inspired Mary Shelley's Frankenstein.