Ki and Gil will enter this room through the first the doors at the top of it. It contains one Mage, eight Mirror Knights and four Golden Mirror Knights.
That first key at the bottom of the room does not open any of the doors at the top of the room, the second key at the bottom of the room opens the fourth door at the top of the room, the third key at the bottom of the room opens the aforementioned first door at the top of the room, and the fourth key at the bottom of the room opens the third door at the top of the room. There is no key for the second door at the top of the room, so there is no way of knowing which room it leads to until you are led back here later in the game through it (and possibly stabbed by one of the Mirror Knights...)
The fourth door at the top of the room leads to Upward Passway (Room Pass: DF2), the aforementioned first door at the top of the room leads back to Sacred Chamber (Room Pass: HF9), and the third door at the top of the room leads off to Trophy Room (Room Pass: HC7). Remember that now.
