The tower depicted below was one of the most frustrating Vista Points I have encountered in Guild Wars 2 thus far. We (myself and a guild member) must have run around the thing 20 times or so trying to find a way in.
Finally, I talked to both of the Charr soldiers standing below it, and one of them said something about flying cows coming from past the harpy nests. We decided that maybe that had something to do with it. So off we went, trudging past the harpies while being careful not to aggro any of them, and what do we find?
A Charr doing an experiment with catapulting cows. We wound up playing an event to save the cows from the harpies, so they could be flung in the catapult instead of mangled by the harpies. Good times. At any rate, around and around the catapult we go until Stefan notices that, hey, on the other side of the catapult from the Charr doing the experiment is a point where you may interact with the catapult.
In you go, and it flings you past the harpy nests at breakneck speed toward the tower shown above. Make sure to do this when you've got enough life to survive the trip. You hit pretty hard on top of said tower. Lesson learned? Talk to the NPCs around seemingly impossible to reach Vista Points in future to save high-level frustration: