Bavaria

One of my favorite spots in Bavaria (my first backdoor) is the Illertal of the Oberallgäu. It starts in Immenstadt im Allgäu, and goes up to the ski resort of Oberstdorf, and you can go beyond that to the Austrian valley of Kleinwalsertal.

From Oberstdorf, you can take the train to Kempten and pick up the Ausserfernbahn train line (Kempten-Pfronten-Reutte in Tirol-Garmisch) to Garmisch-Partenkirchen. Or, you can take the bus from Oberstdorf on a spectacular ride up a hairpin road out of Hindelang to Oberjoch and on to Füssen.

If you don't want to go to Füssen, get off the bus in Pfronten and take the Ausserfernbahn to Garmisch. From Füssen you can go by bus to Garmisch via Oberammergau, or you can go by bus to Reutte and take the Ausserfernbahn from there to Garmisch.

We always rent a car to see Bavaria and Tirol in Austria. The roads are good and very easily driven. You can see four times as much stuff not having to deal with public transportation schedules, and such. We love to make a loop south of Munich, over to Salzburg and back into Munich rambling from village to village up on the mountain sides. And the mountain vistas are beyond breathtaking.
Northern Italy and Tuscany is another place best visited by automobile.

I would also encourage you to rent a car for this portion of your trip. You can pick up and drop off in GP. There are so many small towns to visit and there isn't train service to them. We were there in December and stayed in Partinkirchen at Hotel Schatten. It was the perfect location in the old part of town and a great value.

Don't listen to those people who tell you a car is necessary to travel in Bavaria. A car, IMO, is just a way to make up for lack of planning. I've spend 87 nights in Bavaria on 7 trips in the last 16 year. I plan my stops using the Internet without any consideration how to get there. Then I look for transportation. If I needed a car to get there, I would rent one; I have never had to.

And I have stayed in a lot of small towns. Of 21 towns in which I have overnighted, 10 have had under 12,000 population.

Not including U-Bahn stations, Bavaria has over 1,000 rail stations, so you are never far from one, and their transportation is augmented by an extensive network of local buses, although I have only needed a bus to get to 2 of the 21 towns.

All of the places I mentioned above are easily accessible by rail or bus. The Germans aren't dumb. If there is a place people want to go to, they provide public transportation to it.

Yes, it usually takes a little longer to get somewhere by public transportation than by car (although sometime trains are faster), but saying you can see four times as much is total fantasy.

I have done extensive calculation on the cost of public transportation to wherever I have gone vs. the cost of a rental car plus fuel, and I have find I have saved over $200 per week. Plus I find traveling by train far less of a hassle vs driving.

So that is my recommendation. Plan your trip, then look for access by public transportation. If there is somewhere you really want to go to and can't, ask here. Only if you can't find public transportation should you consider renting a car.

"We don't plan to rent a car and so will rely on the train system."

You will have no problems visiting some nice places by train. Lee has already mentioned a few good options very close to your route. Landsberg am Lech is a Romantic Road town slightly further afield. Between Landsberg and Garmisch-Partenkirchen, the train route south passes through Diessen, a handsome place on Ammersee Lake, just across which lies the town of Herrsching (use the boat there to cross.) Herrsching is a popular starting point for the short hike to Andechs Monastery, which Rick Steves covers in his book and at this page.

Anyone who always rents a car in Bavaria can probably tell you what driving there is like - but not what train travel is like. IME trains are a doable and enjoyable way to see this area.

Königssee. One of my favorite places. I keep going back. Regensberg and Bamberg for a day. Go a few streets over away from the tourists for a Kaffee and a Bier. Eat local food. Talk...

http://www.koenigssee.com/

My suggestions for Bavaria are to visit Linderhof Palace (King Ludwig's hunting cabin with spectacularly landscaped grounds), Ettal Abbey with its beautiful church interior and Oberammergau and Mittenwald with their painted houses, Wieskirche (another beautiful interior) and Fussen home of Neuschwanstein. I would also recommend driving the Alpenstrasse from Fussen to Berchtesgaden and Konigsee.

What I have suggested would fit nicely into the 3-4 days that you have set aside. For this trip I would rent a car. I don't have anything against trains for relatively long hauls between major cities but in this situation you are going through many small towns and past pretty little lakes and I am not sure that it can be done by train. In addition these roads are well built, relatively low speed limit and not unlike the country roads you might drive in most US states - and Germans are good drivers.

I don't have anything against trains for relatively long hauls between
major cities but in this situation you are going through many small
towns and past pretty little lakes and I am not sure that it can be
done by train.

A lot of it can be done by trains, but even more can be done by bus. The RVO bus system, a subsidiary of the Bahn, has a very extensive network in southern Bavaria, shown here of almost 12,000 km with 11,000 stops.

I've been to all of the places you mention. They are all accessible by bus and some, Füssen, Oberammergau, Mittenwald, and Berchtesgaden are also accessible by train. At one time or another, I've been on almost all of the Alpenstrasse. RVO bus 9608 goes from either Garmisch-Partenkirchen or Mittenwald to Kochelsee past a pretty lake, Walchensee, and if you're not driving you get to see it.

The Wendelstein Ringlinie makes two trips daily (morning and afternoon) over the mountains from Bayrischzell, which is accessible by train (BOB), to Oberaudorf on the Inn. That's a particularly scenic and exciting (steep grades) section of the Alpenstrasse..

Two RVO bus lines, 9505 and 9506, go from Bernau to Inzell, near Bad Reichenhall and Berchtesgaden via Reit im Winkl, a small (pop 2600) mountain town near the Austrian border.

Another particularly exciting part of the Alpenstrasse is the hairpin climb up the mountain side out of Bad Hindelang on the RVA bus line 9748 from Sonthofen to Oy-Mittelberg via Oberjoch ski area. It was fun on the bus, but I surely wouldn't want to drive it.