The Cape is acquired by obtaining an Achievement Diary Hood from Twiggy O'Korn located in Draynor Village, south of the bank. He sells it for 99k GP only for players who have had all Diaries completed. Without a certainty, one of the RS gold most difficult things to get in the game because it requires advanced skill levels, but also the fulfillment of various tasks which often have complex quests.
Achievement Diary Cape is cut upon completion of all quests, making the reduced version harder to find. Similar to Quest Point Cape, this item is cut off whenever a new quest comes out. It is only trimmed when all quests in the game are completed. This means that every new mission has to be completed, as well.
Both the untrimmed as well as the trimmed versions of this cape come with +9 bonus to every defensive stat, as well as +4 bonus to Prayer skill, which makes it the best slot-untrimmed cape for Prayer. Achievement Diary Cape also has cheap OSRS GP 10 daily teleport fees to the Achievement Diary Master, which makes it an excellent transport item.