I'm with Adeejay regarding the Nordschleife (Nurburgring) - but even more so I'd say don't go on a bike unless you've made some kind of arrangement to ride it with someone who knows the circuit, knows the rules, and can guide you round for a few laps.
First time I went was in the early 1990's - wasted my time and money - wobbled around with a couple of others who knew nothing about it for 4 laps, just getting in the way of everyone else and being a mobile roadblock. Once I'd had some instruction, it became much easier, I got to know the circuit and started to relax when riding it - arm pump from a death-grip on the bars gets most first-timers. Certainly don't ride it with your bike fully loaded up for a tour (anything goes wrong and you lose everything).
If you must go, for your own sake and so that you don't cause problems for others, learn the rules, prepare yourself mentally and go with someone else, just in case you do bin it its best to have someone around who knows you and can help you.
On your route, make sure you ride the D500 from Waldshut, via Triberg and Freudenstadt, to Baden Baden - awesome route, awesome scenery, fantastic people.