After passing the fourth vision of the woman/fifth note, you'll be almost at the end of the road. Keep an eye out to the right of the road, and you should be able to make out a grave marker past and between a couple of trees. If you're having trouble finding it, go to where you can see the fifth vision of the woman, turn around, and look to the whilst going back whence you came. It shouldn't take long before you spot it. Once you do, move up to it and see that there are three graves. In the middle of them are a bunch of flying lights/wisps. Just walk straight into them, and you'll get a speed boost for a short amount of time. The achievement will pop.