The Return of Ishtar/Locked Room


 * Ki and Gil enter this room through the door at the right of it. It contains five Orange Vampires and ten Purple Bats (both of which take four hits to kill).
 * The key at the bottom-left of the room opens the aforementioned door at the right of the room (there are no keys for the doors at the centre-left and top of the room). Therefore, there is no way of knowing which rooms those other two doors lead to - until you are led back to this room through one.
 * The aforementioned door at the right of the room leads back to Observatory (Room Pass: YC9). It would appear that the "DON'T ENTER BE GONE" sign in that room was there for a reason - because you will just have to go back out the way you came in, risking your life to collect the only key for it.