Dortmund has become a center of high-tech industry, but back in the day, it was one of Germany's first brewing centers, and Dortmunder beer is definitely worth tasting in a local bar. Visit the Reinoldkirche or the Marienkirche, or venture south of town to the ruins of Hohensyburg Castle. December is an especially festive time to visit Dortmund—one of Germany's biggest Christmas markets takes over the center of town.