The Letters of the Lost are the focus of Far Cry 3's Dead Letters Trophy/Achievement. To unlock this piece of digital showmanship, you just have to find all 20 letters and collect them. This is a lot simpler than it seems, especially when you consider that the collectible maps are available for purchase at the general stores.
If you're super cheap or some kind of horder, you can use the video above to find the Letters of the Lost and unlock the Dead Letters Trophy/Achievement.
The sequel to the award winning Hellblade: Senua’s Sacrifice, Senua returns in a brutal journey of survival through the myth and torment of Viking Iceland. Intent on saving those who have fallen victim to the horrors of tyranny, Senua faces a battle of overcoming the darkness within and without.
