Red Dead Redemption
91 Achievements
40-50h
Into the Sunset
Complete "The Last Enemy That Shall Be Destroyed". Details for this achievement will be revealed once unlocked
20.4%
How to unlock the Into the Sunset achievement in Red Dead Redemption - Definitive Guide
This is the last story mission of the epilogue and though it does not end the story exactly there is a dramatic change in the game, and YES you can continue to play after this achievement is complete.
While it is worth the most points it isn't the end of the main story; there is a mission with a stranger in Blackwater(after you unlock this) that will end the story.
There may be spoilers in the comments.
Story related and cannot be missed. This trophy will unlock as soon as you finish this mission "The Last Enemy That Shall Be Destroyed". For a detailed walkthrough see below:
This will be the last main story mission in the game and has a lot of cutscenes. As soon as the mission starts you will have to take out hordes of enemies coming up the hills. Uncle will help you until he tells you to get inside and trigger another cutscene, then you will fight another two waves of enemies coming from the north side of the map. After these waves John will tell his family to get in the barn. There will be yet another wave of enemies with rifles that can kill your family so stay close to them and take them out. Once you get to the barn there will be a cutscene and the mission will be over.