This is attainable in either Goat Ville or Goat City Bay.
You can unlock this anywhere you are not at risk of being hit by a car or walking into objects/people. Manual means to walk on your front legs for a certain distance (this is a reference to Tony Hawk games). For this achievement, you need to walk a total of 3,000 feet without falling over.
First, find an area you can do this safely. Walking across the field or down the sidewalk are good locations. To walk on your front legs, press
back then immediately forward. As soon as you start to walk on your front legs, press
to activate Slo-Mo (or you can do this before you start walking). Then move
to keep the line in the middle of the meter. In Slo-Mo, this is quite easy. If you need to turn, use
to rotate the camera. Once you’ve gone 3,000 feet, press
to jump. Once you land on your feet, the achievement will unlock.