Make sure you sit at the bench, head down the glowing tunnel, and defeat it in order to unlock a new ability. Play the Elegy of the Deep here, and then use the Silk Soar to make your way into the coral tower area. Head left and up the wall to start your first fight in a series of gauntlet fights. Once the room is cleared, Silk Soar up to the boss arena. From here, silk soar up, and follow the path marked on the map below.