For this achievement you need to reach 200MPH (320KPH) on the Nurburgring in a Modern Grand Touring car, the car I suggest is the Nissan GT-R Black Edition, which you can rent in free play for free.
From the main menu choose Free Play and setup a race on the Nurburgring - Nordschleife and choose the Nissan GT-R Black Edition by either renting or using your own. Then once the race starts turn around and head round the track backwards which will bring you straight to the 'final' stretch of the track which by going backwards is downhill, the GT-R is a very powerful car and has no problem getting over 200MPH.
Once you have reached 200MPH you can quit the race and your achievement will pop.
Here's a video of the GT-R reaching over 200PMH.