Car Rental

So, we decided to ditch our travel agent because she was NO help. She just wanted to put us on a cruise ship. Instead, we took up the task and booked 4 nights in Munich, 5 nights in Florence and 4 nights in Rome for 9 people. So, everything is done except transportation.

It would be a simple matter of buying point to point rail tickets to our destinations, except that our group wants to do different things while we are in our locations.

My friends and I will be heading to Europe next summer. On our itinerary, we are scheduled to travel from Frankfurt to Munich. I think it would be a good idea to travel this route by car (autobhan) instead of train to experience the autobahn for ourselves and to get a break from trains.

That being said, what does an American need to do to be certified/able to rent a car in Germany? Also, the high speed limit of the autobhan obviously is one thing we want to safely enjoy (being 22 year olds), but is it worth it?