If you enjoy driving: San Bernard Pass and Gotthard Pass (go over, not through the tunnel). You´ll be passing the weather watershed between north and south of europe on either. Going up on the north side in fog and breaking through to sunshine on the south side and going down towards Italy and the mediterean. Plenty of other lovely passes as well. Southern Germany, Austria and Switzerland are wonderfull drving countries.
If you are a seriously good driver in car that you know well, here´s a little hidden gem: Find "Arosa" on the map of Switzerland. It´s a smaller ski resort a bit off the usual tracks. The last 30k of mountain road to Arosa (climbing from 600 to 1800m) are probably the most fun I´ve ever had (in my 2005 330Ci SMG, since stolen). No point in driving it at normal times. Get up before dawn and start your ascend of the last 30k just when daylight ist breaking so you can see enough (too dangerous to really push hard in the dark) and there is no traffic. Poinless chugging up it behind another car or truck. But with a clear road and early daylight...
+ it´s a dead end. So you get to turn around once you´re up there and get to have the same fun going down...
Belgium and Netherlands are pretty boring to drive through. So for scenic driving stay south as long as you can. When you do go north, stay easterly in Germany for longer (France is pretty boring outside of Paris as well and very dull to drive through) and pass through Heidelberg (a bit of a cliche though), go over to the Nurburgring (but don´t drive a rental on it, it´s not covered by insurance). Instead go to one of the spots to watch and see lot´s o people overestimating their driving skills on the Ring.
Further north Cologne has a nice vibe but is not much too look at. Duesseldorf is very nice (and still on track to getting to Amsterdam)
In the southern parts of germany there are some very nice technical museums (one in Sinsheim which is very fine). Less of WW2 museums in germany (or Austria or Switzerland) for different reasons. Obviously all references to WW2 in Germany would be pretty glum. So for nicer museums of WW2 you´ll have to pass into the UK. They have reason to celebrate it.
Not on your route, but the most fun and interesting city in Germany is probably Berlin. Prag is fun too. Munich is pretty to look at but very "square". Don´t like the people there. The Bavarians in the coutrieside are much nicer (rednecks but nice). Avoid Stuttgart. Claustrophobic and depressing. Only good thing about that area are the Porsche and Mercedes museums.
Good luck with getting a 1. Most rental company do not, will not guarantee a particular make or type of car, only a rental car class and you may end up with a Peugeot 308SW as an euqivalent of a 1 series. Which of course to anyone with an interest in driving could not be further...
