First you will need to enter the Cavefish lair (see Gogglor achievement). Once inside, drive Ben to the right. On the next screen, drive to the bottom left. You will arrive an area with the ramp. Use your hands once on the ramp. Ben will move it. If you pay attention you will notice the ramp pops off one of the road bumps. Use your hands again on the ramp to attach it to the bike. Now drive the bike to the right one screen. Ben will stop right before the lit tunnel. At that point, use your hands on the ramp again. Ben will push the ramp and it will pop off a few road bumps. Then you will get a cut scene where the Cavefish bikers crash. After that you will appear at the gorge and the achievement will pop.