Flintlock: The Siege of Dawn

Skulls are found on interactive pedastals that create rifts in the sky for you to travel across the map quickly or reach areas you normally would not be able to. You will find well more than 50 just getting through the story, side-quests, and collectibles, so you will unlock this naturally going for the rest of the achievements. When you get close to a skull, your controller will begin shaking fairly violently to alert you that one is nearby.