The strange relic is located in chapter 15. Part way through the level you will eventually reach an area where there is a wooden door which cannot be opened. You need to go on with the level and get to the other side of the wooden door to let Chase in. In the area where you do this look opposite the wooden door. On the wall to the right is a bit you can climb up, simply climb up and it will be at the top. This trophy will unlock as soon as you pick it up. See the treasure guide here if you want a video location, look for the chapter 15 video.