When you first enter the room with Oka's Chest, there are some yellow banners that light up on the wall. Make note of what you see on the banners (something like a krok head, a snake, etc.). Then go to the same items on the floor and light them up.
In case the banners go away before you got to see them, just back out of the room and re-enter. The banners will light up again.
