To do this, you have to approach a safe and simply hold
to start cracking it. You do not need to grab the loot from it if you don't wanna stick around for a minute or so and wait. You need to do this a total of 5 times and there's only 1 safe per match.
The safe can be found on the map under a light blue icon called "Barred house". Once you get inside, you will notice that one of the doors or windows is "barricaded", just hold
each time for a total of 4/5 times to completely remove barricade to get inside the room, the safe will be in it. This achievement works under the tracking.
Important note : There's only one safe per match, and when it's getting unlocked, whether it is by you or another outlander, it'll prompt a message on the screen for EVERYBODY I'm the game that states "Safe is being unlocked". So everybody will look at the map and know where you are, or you know where they are. But if you get that message while heading there just don't bother, you need to be the first one to start the process of unlocking for it to count. Progress will track immediately after you hold X on it as it is closed
You just need to be lucky to get a close spawn to the barred house, as that is random for every game and can appear in whatever house around the map. Good luck.