Might want to add the link to the thread where the guy put the picture of the location of the Final Riddle - Spirit of Arkham. I noticed multiple threads in here the last few days asking about the location. This thread is the best one I have seen (it is literally idiot proof
). Although he needs to note in his post you have to scan it after you gather all the Riddles and you should have 1 Chronicle of Arkham left just in case somebody does not know the requirements for the achievement.