Walhalla (11 km [7 miles] east of Regensburg) is an excursion you won't want to miss, especially if you have an interest in the wilder expressions of newfound 19th-century pan-Germanic nationalism. Walhalla—a name resonant with Nordic mythology—was where the god Odin received the souls of dead heroes. Ludwig I erected this monumental pantheon temple in 1840 to honor important Germans from ages past, kept current with busts of Albert Einstein and Sophie Scholl. In keeping with the neoclassic style of the time, the Greek-style Doric temple is actually a copy of the Parthenon in Athens. The expanses of costly marble are evidence of both the financial resources and the craftsmanship at Ludwig's command. Walhalla may be kitschy, but the fantastic view it affords over the Danube and the wide countryside is definitely worth a look.
A boat ride from the Steinerne Brücke in Regensburg is the best way to go. On the return trip, you can steer the huge boat for about half a mile, and, for €5 extra, you can earn an "Honorary Danube Boat Captain" certificate. Kids and adults love it. To get to the temple from the river, you'll have to climb 358 marble steps.