Alright, so from the big area near the beginning with the three staircases, go up the one to the southwest. Follow the south path all the way around, past that chest reachable only with Nash, to another two staircases, go up either one, and then go east, south, and then west past a staircase and then past a doorway, and you will come to a small room with several enemies. The chest to the west is the one that contains the Heart of Benevolence. Hope this helps!