Descend from the gong area and make for the far-left corner. Jump to it and climb down. Turn left and drop off the ledge to the square below. Drop off that square to the ground. Turn around and pull the switch - the door in the building next to the Ice Palace is now open. Climb back out - and when you're at the top of the ladder, backflip to the niche carved in the snow. Claim the dragon, then loop around to the front of the Ice Palace. Hug the outside wall as you make your way up the outside of the palace to the gong area. Get ready to finish off this mission.