This video shows you how to get Golden Chest #3, which is hidden in Angry Birds Rio High Dive Level 6. The chest is immediately under the slingshot platform. Fling the Boomerang bird backwards and spin him back to reach the chest.
Recent Walkthroughs
There appears to be only one way to get the chest with the boomerang bird as shown in the ABN video. It took me two birds because I hit the structure with the first.