november_moon: I like DIY trips too, although the distances covered are greater usually - like two or three countries on a driving trip. Usually my friends or family will do an area in one country and then drive and do another area in another country - like drive the Romantic Road in Germany and then return to Paris and do a side trip somewhere.

Rarely but on occasion, especially if I have some time to myself, I like to just park myself in a big city and do some side trips on my own. Last time I discovered Graz while daytripping from Vienna. Really wish it had been for more than one day - but then it means I'll just have to return to Graz some day. :)

If going mainly to large cities as previewed in OP then IMO take the train, right into the city centres and use superb public transportation to get to your hotel or stay in a hotel near the station as there are often several to chose from. Parking is really expensive and city centres are often pedestrianized.

anyway if doing more than a few rail trips consider the bargain IMO German Railpass - or Twin pass if two folks traveling together - German trains are amongst the finest in the world - up to 2-4 departures hourly between most main cities and even good service to Rothenburg/Tauber.

Great sources of info on German trains and railpasses - www.budgeteuropetravel.com; www.seat61.com; www.ricksteves.com. Go to www.bahn.de for schedules and prices to compare to the railpass - there are online discounts if you want to lock yourself into a specific train weeks in advance (sold in limited numbers and discounted tickets can sell out early) but with a railpass you can just hop on any train anytime in Germany as no trains you will be taking require reservations - so full total flexibility the railpass is great - and these fully flexible tickets often cost a ton so a few trips make them pay off.

Finally for the average tourist on the trip of a lifetime pay the extra IMO and IME of traveling on German trains for decades for first class - lots more empty seats - easier to store luggage, bigger seats, more window seats, etc. and conductors will even bring snacks and beverages right to your seat. A railpass especially costs relatively little more in first class than second class - 2nd class can at times be SRO but never so IME in first class.

the Wunderbar www.bahn.de German Rail web portal is so so fab - it will even tell you which tram or bus to take from any address like your hotel to the nearest train station!