Looking at the map in the orientation of North at the top of the screen... Find the circus in the middle left or so of the map. then North East of there will be a building with a ramp from the ground to the roof. drive up the ramp at a normal speed, and drive across the roof onto the next roof. Turn right and go to the end and turn right onto another ramp. go strait and turn right around the corner of the wall on a narrow ledge. just keep following that and you will see a red fish on a stick (haha fish sticks) and just drive into it causing it to break and there goes the 100 G achievement.