This is gained in the Before Outbreak map. Following the title update that added the hub world to select a map, this is the "GOATZ" with the green background. You'll know it's the right one if you begin in a coffin and not a cage.
From the spawn on this map, head straight ahead over your gravestone and the fence and you'll come across a road that goes off to your left. Follow it to the nearby Whiplash amusement park. You should notice a large pool with a Ninja Warrior course set up in it, and to get this achievement you must first pass through the START ring and then the FINISH ring without touching any water.
Obviously, you can cheat as much as you feel like with mutators like anti gravity or flappy goat. If you don't feel like putting in that much effort, you'll get to a square cyan platform near the beginning of the course after hopping on two bouncy red balls. Just wait here until it launches you off the course, then go walk through the FINISH ring for your achievement.