Planning a trip to Germany flying in and out of Frankfurt or into Frankfurt and out of Munich next May (5/18-5/28). We will be meeting our daughter in Frankfurt after her May study abroad program. She will be visiting Mainz / Heidelberg / Stuttgart and Basel. We do not really want to rent a car. Looking for suggestions on travel. Should we pick a base of operations and plan day trips or travel through out the region spending a night or two in different areas/cities? Thanks.
Mark