Heidelberg is one of Germany's towns not largely destroyed during WWII - some say because the Allied Command had chosen it to be their postwar HQ

Anyway this lovely town on the Neckar River has the castle of your dreams plopped on a hill above it

and the presence of one of Germany's preeminent universities adds a lively flare to the place

From Frankfurt about an hour i think by train - perhaps have to change at Mannehim - lots of trains just by tickets at station.

www.bahn.de for train schedules (German rail website)

I second Heidelberg.

For the other leg, maybe some impressions of the Rhine?

I would suggest renting a car. Then drive westwards to Eltville and up to Kloster Eberbach. It is an interesting monastery ("The Name of the Rose" was filmed here) and as well a very famous vineyard. Also good for tastings.

http://www.klostereberbach.de/html_english/index.html

Then drive a little more westwards to Rüdesheim. The small village is the entertainment capital of the Rhine valley, but still picturesque and a good place to get some food and wine.

Here, the scenic section of the Rhine valley begins. You may drive a few kilometers northward along the river to see some scenery.

Return whenever you want. It will be a nice daytrip. On the way back, you may warm up yourself in one of the spas of Wiesbaden.

http://english.wiesbaden.de/index.php

(Go to "Living in..." -> "Recreation" -> "Wellness")

BTW, Frankfurt is an interesting city too. It has some very good museums and a nice nightlife scene (in Sachsenhausen).

Rhine would be great too IMO

KD boats do run once or twice daily thru the Rhine Gorge and stop at several cutesy towns, villages and castles - and trains go on both sides of the Rhine in case you are not into renting a car.

www.k-d.com for boat schedules - reservations are a must in winter to guarantee the boat running.

I'm weary of renting a car and would rather go by boat or train along the Rhine. If I go to Mainz and Bacharach, should I go all the way to Koblenz or make a side tour to Trier?

Will the boat be fine in November? I imagine the weather would be quite unreliable this time of year.

Let me recommend my dear old Marburg again - an easy day (or even half day) trip by train, one hour North of Frankfurt.
More: http://www.marburg.de/detail/24679
The historical centre is really as romantic as the photos suggest, and there are hardly any tourists, which is IMHO an advantage.

Frankfurt is a major train hub and thus a great base for day trips (IF our dear DB and their locomotive drivers finally settle their fight and go back to normal...), so I'd recommend staying in Frankfurt and setting out from there every morning. There are plenty of options you can do as day trips without dragging your luggage along and moving into a new hotel every night. Würzburg, for example.
And, of course, Heidelberg, although "the castle of my dreams" would not be in ruins like the one there.
Same goes for the other places mentioned above.

I do not think, a boat trip in November would be a good idea. If it rains (and the probability for rain is high) you will see nothing. And it will be cold on the ship (outside the cabin).

But you can take the train. From Frankfurt Main Station to Eltville there is a direct train that takes 54 min (via Mainz and Wiesbaden) and another 14 min to Rüdesheim.

Look up the map under www.viamichelin.com and then the train schedule under www.bahn.de

BTW, nothing requires planning in advance. When you are there, the hotel concierge will help you with details.

Oh yes, Würzburg is just 1:10 from Frankfurt by train. And the castle is splendid (UNESCO World Heritage)!

http://www.wuerzburg.de/en/index.html

That's an interesting idea -- to stay in Frankfurt the entire time. Which hotel would you recommend for those purposes. I'm a female alone and i was a bit concerned that the redlights district is right by the train station. So should I still find a place near there? Also, should the trains be on strike, is the bus communication pretty good?

Not far from the train station is the Hotel Bristol. Rates under 100 euro and a good breakfast. Frankfurt's red light district is pretty tame compared to many european cities. Avoid the obvious areas at night and you will be fine.

Frankfurt is easily diregarded by many on this board, but there are many jewels to be found in and around Frankfurt.

For Frankfurt hotels, use www.hrs.com.

I personally like the Hilton (which is one of the world's best Hiltons), but of course it is a matter of budget.

If forget to include the link to the Frankfurt website:

www.frankfurt.de