I have heard the Schwarzwald-Hochstraße is a famous and challenging road. starts at like 250m and ends up near 1100 meters! Nice round abouts going up the mountain passes.
http://www.schwarzwald.com/hochstrasse/
I have always wanted to drive the old Glockner Pass (Großglockner Hochalpenstraße) thru the Alps (Germany/Austrian borders). I have always had a thing for the old Silver Arrow cars and they raced in this area. Ferdinand Porsche also test dorve the first batch of Beetle (KdF wagon) cars on this pass - I believe. Now a days the modern Autobahn takes you around the old mountain passes of yesteryear.
http://www.grossglockner.at/en/hochalpenstrasse/
But for me... since I live in Bayern... and really in Franken-land... my first choice to get lost is always in the Frankische Schweiz, right in my very own backyard! This is the area between Nuernberg/Bayreuth/Bamberg. basically also the Bier (Beer) Capital of the world bc we have so many Breweries in this area. You can look that up in the Guniess Book of Records! lol
http://www.fraenkische-schweiz.com/bilderbogen/en.html
take care,
David