Originally Posted by SteeminHotKarl
Um.. Not sure what I did but I found an extra chest in between #56 & #57. It was right above the save point, before using the chain to tear down the wall. The achievement popped before getting chest #63. Lucky I guess
Same here, neither of the collectible guides mention it. I did, however, look at a walkthrough on gamefaqs and he mentions it there so idk.