Climb the highest point in Naval Strike
The highest point in the Naval Strike expansion can be found on the Wave Breaker map. This map features a large island cave in the center of the map, which houses a submarine. You can climb on top of this island near the B flag, and then make your way to the highest peak, which is on a rock to the North of the three electrical towers. Stand on the rock for a few moments to unlock the achievement.
Here's a video by HarryNinetyFour: