Across the Danube from Regensburg, on the high ground to the east, stands the Walhalla, a Greek temple in the middle of Bavaria. King Ludwig I had it built in the 1830s and 1840s as a hall of fame for great Germans, and its white marble columns, set on a hill above the river, look odd and wonderful. It is a short ride from the old Roman camp, and the two make an interesting pair, the Roman soldier's frontier and the nineteenth century's dream of antiquity.
The Roman camp itself, Castra Regina, lay on the south bank, on a low terrace above the river. Its walls, gates and streets were laid out on a grid, and the northern wall ran close to the Danube, with a view across the water to the barbarian lands beyond. Today the Roman layers lie beneath the old town, but they show in the plan: the street called Unter den Schwibbogen follows the line of the northern wall, and the Porta Praetoria, the northern gate, survives in part in the old town.
Riding out to the Walhalla is a pleasant afternoon. The road runs along the north bank of the Danube through Donaustauf, a small town with a castle ruin above it, and climbs to the monument through woods of beech. The surface is good, the bends are easy, and traffic is moderate, though weekends can be busy with visitors. The view over the Danube valley from the steps is wide and calm, with barges moving slowly along the river.
Regensburg has plenty of fuel and food, and Reinhausen, a suburb on the north side, has a few stations. If you want a snack, the historic sausage kitchen near the stone bridge grills small bratwurst over beechwood and serves them with sauerkraut and sweet mustard, and has done so for centuries, so it says. Wine from the hills around is light and crisp. Spring and autumn are the best seasons, when the air is clear and the crowds are smaller. Climb the steps slowly and look back at the river.