This is yet another collectible achievement and this time you're going to collect witch trials history plaques. They can be found in three different areas and are nine in total.
One is found in the town of Salem, close to the Judgement House. Seven is located in the Museum and finally one inside the Judgement House.
I recommend using Maka91's excellent video guides for all of the collectibles but I will be adding a video from Redemption Mode just because it shows how to get this specific achievement. So I take no credit for the video.