Nordlingen

Nördlingen takes 1 day to see: the complete circular medieval walls, walkable in their entirety around the whole town, are the main reason to visit. April-October is best. It's inexpensive by German standards. It's built entirely inside the Ries crater, left by a meteorite impact 15 million years ago, and the crater's own rock -suevite, which contains tiny diamonds formed by the impact's pressure- was used to build much of its historic buildings, including the tower of St. George's Church.