One of the strangest mysteries in archaeology was discovered in the Diquis Delta of Costa Rica. Since the 1930s, hundreds of stone balls have been documented, ranging in size from a few centimetres to over two meters in diameter. Some weigh 16 tons. Almost all of them are made of granodiorite, a hard, igneous stone. These objects are monolithic sculptures made by human hands.
World Mysteries - Strange Artifacts, The Stone Spheres of Costa Rica