Stuttgart, Germany: Porsche Museum
It was left up to me to decide which manufacturer to spontaneously visit while driving through Germany. Porsche and Mercedes Benz are both in Stuttgart, while BMW and Audi are in Munich. VW is a bit out of the way.
Beyond their automotive prowess, I have always been fascinated with Porsche's dedication to the 911 as a designer. More than sixty years of iterative refinement to a single model is extremely appealing to me and makes me think again about legacy and master of a singular craft (e.g. yesterday's Taittinger Estate visit).
*Pro tip: Each manufacturer has a factory and museum. Factory tours require reservations so book in advance. More advanced homosapiens will throw money at a German cashier to reserve a performance car (e.g. 911 or M3) to drive on a track.