To get the GW2 Blasted Moors vista, begin by talking to Jager Haunteyes and Korin Hauntfoe, a pair of NPCs at the base of the tower in Blasted Moors. They will tell you they have seen cows flying through the air.
Korin will mention that he suspects the cows are being launched by an engineer southeast of the tower, on the other side of some harpy nests.
Head southeast. Run past the harpy nests until you spot an NPC named Mad Mardine who is working on a "Cattlepult." This is, as you might have guessed, a catapult designed to fling cows into the air.
Click on the cattlepult and you will be launched to the top of the tower, where you can access the vista.
Note: If you don't have a glider, you will need to waypoint down. It is too far to jump, and there are no stairs down to the ground.