Vacationing in Europe. Where should I go?

[loadedstatement]

Hey VGC, Im taking a trip to Europe in the next couple months. My main base will be in Germany.  My girlfriend lives in north western part of Germany (in Melle) and her family lives in southern germany (in Schwäbisch Hall).  I will be there for 2 weeks and want to spend a good deal of it in Germany.  So here's the deal. 

In Germany, should I go to Osnabrück, Baden-Württemberg, or Berlin?

Outside of Germany (for little side trips), should I go to Asterdam, Brussels, Prague, Vienna? (Or do you have another suggestion?) I'll probably go to 2 big cities outside of Germany.

NOTE: I dont want to go too far from Germany.  I will only be riding the trains while in Europe.  And Italy is out of the questiion.  Im going there on a separate trip :)