Remember the old riddle...from the oedipus cycle. Man...is the answer. when you are a baby you walk crawl (4 legs), when you are and adlut you walk on two legs. and when you are old you walk on 3. (a cain.) so look at the surrounding doors....the # of red stones it has on top is the # door that it is. the pattern is just like the riddle, 4-2-3.