Nurburgring Professional Achievement
Earn 20 gold medals on Nurburgring in Career.
As with most DLC, the Nurburgring will either be added to your Career-events or replace an existing event. Depending on your preference of car, you can find the appropriate events from your Career-list and browsing through the events.
For efficiency, you should combine this with "The German Connection." The faster car you choose on the Nurburgring GP circuit, the faster this should unlock. I recommend the Series League, S Class Series using any S Class car from Audi, BMW, Mercedes-Benz, or Volkswagen.