The last set of tracks you unlock are entitled "Desert Paradise". Very similar to all the other ones, except your riding on sand. The achievement requires you to finish all the leves in this set of tracks (obviously stated in the achievement description)
I'm mostly here to talk about a certain level called Turn Around...level 19. This is the most frustrating level in the entire game and will make you want to destroy your phone. Hopefully you don't.
Right at the beginning it puts you in a tight landing with some spikes that just about always catch you, yet you have to jump and flip upside down to catch a rail.
There are 2 tricks I want to share that will hopefully ease the pain.
1) Just before you launch from the ramp, swipe downwards (crouch) done right, this will slow you down so you have enough room to land and jump.
2) As frustrating as it gets...I recommend if you don't nail the landing on your first try. Reload the entire game. I found that for some reason he hits the ground far enough away from the spikes using tip 1 more often then when I try to just retry.
After you successfully jump the spikes remember to quickly flip your guy upside down to grind the rail. Stay upside down, jump to the next rail, and again to the next. You will go up and around and into your first check point. From here on out, the level is easy.
It only took me about 300 tries to get this damn level :) (yes...three hundred)