My husband and I are doing a home exchange to Frankfurt, Germany with our kids (boy age 9, girl age 6) for the month of July. We will have the use of a car and speak German. I am looking for some ideas for places to visit (day trips or overnights) that would be of interest to the whole family. While castles and cathedrals are definitely on our list, we don't want to put them in a castle/cathedral coma! We are a physically active and adventurous family. Any suggestions would be great! Thanks!