This achievement requires you to unlock each individual track for use in Free Race. To unlock a track, you have to complete a race on that track in Off-Road Masters.
The tracks in the game are as follows.
Unlocking tracks will come naturally as you progress through Off-Road Masters. However, you will not get around to unlocking the achievement until you get to the Final League episodes. If you're doing all the races in order, the last track you will unlock is Mont Blanc
- Long Layout in Episode 14 (Drivers On The Storm).