Visit every location of the game.
This requires that you visit every location in the game at least once. You don't have to do anything while you are there. When looking at the main map, locations have a downward arrow mostly surrounded by a circle and are one of five different colors as detailed below:
- Grey - unvisited
- White - visited (named locations count, but not individual chests, fishing locations, etc.)
- Red - fort that has not been captured
- Green - fort that has been visited and captured, but not fully explored
- Gold - visited and fully explored
There will be other items on the map as well that are not locations and as such do not count. These include but are not limited to naval convoys, legendary ships you have yet to beat, individual chests and other items, harpooning locations, and ships you can attack.
Note that many locations are unlocked through story progression, so you will not be able to unlock this until you start Sequence 10, Memory 3 at the earliest.