My wife and I are planning a 12 day trip to Belgium, Germany and the Netherlands. After arriving in Brussels we will drive to Trier for two days. Then drive to Koln to tour the cathedral for an afternoon, overnight north of Cologne, followed by three days driving between Koln and Hamburg before we return to the Netherlands and Belgium for the remainder of our time in Europe. We are seeking suggestions for overnight stops in smaller towns and villages with scenic drives along the way.
"...in smaller towns and villages with scenic drives along the way." That depends on which rote you take after leaving Köln. The closer places I would suggest are Münster/Westfalen, more of a city than a town, and Soest/Westfalen. If you intend to veer more to the east in the direction of Hannover, then my number one choice for a town (historical) is Minden an der Weser, a very nice and relaxing place, worth the detour. Of the three here, I liked Minden the best, the most interesting.
If you're going to Hamburg via Hannover, then the north of it is a small town well worth seeing ( I haven't been there, only at the train station to transfer).... one reason it wasn't destroyed in the war and its good museums....Celle.
From Trier, you could drive along the Mosel, and at Koblenz, head north along the Mittelrhein up to Bonn. This isn't the part of the river that everyone rages about, but it's still pretty scenic (except for a short industrial strip immediately to the north of Koblenz, that is). After Bonn, the Rhine could be any other river.
From Köln, to the north and northeast (not so much immediately east), the scenery is relatively flat and industrial. This is the most densely populated region of Germany, but not exactly the most beautiful. Depending on which route you take, once you hit either Osnabruck or Hannover, this takes you into the flat heath country of northern Germany, which by contrast, is rather sparsely populated. I've driven through this region, but haven't explored very thoroughly. I don't want to write it off, but other than Oldenburg and Bremen, there doesn't look like a whole lot of stuff to see (other than the heathlands) until you reach the hinterlands of Hamburg. I've heard good things about the Ostfriesischen Islands, but this is out of your way on the way to Hamburg (but maybe not on your way back to the Netherlands).