Looking across Lake Constance from its lofty perch, Burg Meersburg is an archetypal medieval stronghold, complete with keep, drawbridge, knights’ hall and dungeons. Founded by Merovingian king Dagobert I in the 7th century, the fortress is among Germany’s oldest, no mean feat in a country with a lot of old castles. The bishops of Konstanz used it as a summer residence between 1268 and 1803.