This achievement is actually pretty simple, it just involves a lot of running around. To get this achievement you need to hunt down and kill all Knights of the Flaming Rose otherwise labeled as "Fallen Knights" and loot the main chest in each camp. People it seems have had the most luck getting this by starting a "New Game" and selecting expansion only, and then going to kill and loot the camps.
There are a total of 8 bandit camps THAT ARE CONFIRMED to be needed to get the achievement.
(If you cleared all the camps go back to each one as you might have missed a guy running around, the easiest place to miss a guy is LOCATION #2 as There are a few on the outskirts of the camp.)
(Clear the guys as close as you can to the center of the camp. *credit to Joueur*)
Below are the locations of the camps.
#1. (Bandit Camp) Straight north of the "Upper Mill".
#2 and 3. (Bandit Camp) North of and Southeast of Zuetzer Castle fast-travel post.
#4. (Bandit Camp) Southeast of Est Taiyar fast-travel post.
#5. (Bandit Camp) West of Erde fast-travel post.
#6. (Bandit Camp) Northwest of Sarrasin Grange fast-travel post.
#7 and 8. (Bandit Camp) Both are to the Northeast of the Bowdon fast-travel post.
If you have any questions or think I may have left a spot out just leave a comment, :)