Nördlingen sits in the middle of a hole in the ground, and the hole was made from space. About fourteen and a half million years ago, a meteorite crashed into this part of southern Germany and left a crater about twenty-five kilometres wide, the Ries, now a gently bowl-shaped plain of fields, villages and low hills. Nördlingen was built inside it, in a perfect circle, and the medieval wall that surrounds it is almost round, the only fully preserved ring wall in Germany that you can walk along the top of. The walk takes about an hour.
The tower of St George's church, called the Daniel, rises ninety metres above the market square, and you can climb its stairs for a view over the red roofs and out across the rim of the crater. The church walls are made of suevite, a rock formed by the impact, which contains tiny diamonds, too small to see and too small to sell. A night watchman still calls out from the tower every half hour on summer evenings, a custom that dates back centuries. In 1970 the Apollo 14 astronauts came here to study impact geology before flying to the Moon.
The Romantic Road passes through, and Nördlingen is one of its best stops, with half-timbered houses, small squares and a cheerful, unpretentious atmosphere. The riding between Dinkelsbühl and Nördlingen is quiet, along minor roads over open farmland and through small villages. Surfaces are generally good, bends are broad and easy, and the main hazards are tractors and the wind, which sweeps freely across the crater plain. The edge of the crater is a low rim of hills, and you can see it from several vantage points.
Wallerstein, four kilometres away, has a striking rock outcrop with a former castle site and a fine Baroque church. Nördlingen has fuel, bakeries and a good choice of restaurants, and menus here lean on Swabian and Bavarian staples, from Spätzle to roast pork. The town is small enough to walk across in twenty minutes, so leave the bike at a car park outside the wall and wander in. Evening is best, when the tour groups have left and the stone glows in the low light.