As you cast Riddle Door, you must specify a riddle. When you do so, you immediately forget the answer to that riddle. Until the Riddle Door is dispelled, you cannot remember the answer to the riddle for more than 10 minutes at a time. A successful DC 40 Knowledge check with an appropriate Knowledge skill will always give you the correct answer to the riddle. Experience Cost: It costs 10 points of experience to cast Riddle Door.