As soon as you arrive you can find 9x Ancient Bones just down the ramp. Kill the Yakshinis then the group of two Yakshas and a Yakshini in this room. Nearby is another Menhirrim with another quest which requires you to hunt a mark; the Mushussu. The mark is just to the left of your position, signified by the star on your minimap. See here for strategy details. Your reward is 6x Moonblossom Seeds .
Return to the fourth floor once you’ve finished here.