Located in the Diquis Delta of southern Costa Rica and locally known as Las Bolas or the Balls, the giant stone spheres are a collection of some three hundred polished stone orbs, some dating as far back as AD 600. Sculptured mostly from granodiorite, an igneous rock similar to granite, the spheres range in size from a few centimetres to over two metres in diameter and weigh up to 16 tons. Since their discovery in the Diquis Delta during 1930s, they have been uncovered in a number of other locations, including the Isla del Cano.

The story of the discovery of the spheres started in the early 1930s, when the United Fruit Company was searching new grounds for their banana plantations. While searching the Pacific side, they found promising land within the Diquis Valley, which is not far from the coast and suitable for export business. However, as the workers started clearing the land in preparation for planting, they discovered some strange stone balls. The most striking thing about those rock spheres was that many of them appeared to be perfectly round and very smooth. The workers rolled them off to the sides of the fields by hand or pushed them using bulldozers. Eventually, many of the huge balls were transported to private or business houses to be used as lawn ornaments.

At some point thereafter, inspired by a rumour that gold is hidden in the core of some of the stone balls, treasure hunters began to drill holes into them, even inserted dynamite sticks inside the drilled holes and blow them pieces hoping to get the hidden treasure. They were frustrated, as they found nothing inside the balls, however several of the spheres were thus destroyed, before the authorities intervened in the matter. Nevertheless, some of the dynamited spheres were reassembled later and are currently on display at the National Museum in San Jose.

Shortly after their discovery, the first scientific investigation of the great spheres was undertaken by Doris Stone, a daughter of a United Fruit executive, who subsequently became the director of Costa Rica's National Museum. While it is widely accepted that the stones are the work of an ancient indigenous people, skeptics argue that primitive people with basic, non-metallic tools could not possibly have made such perfectly round and smooth stones. Myths and wild stories also came up about the spheres suggesting that they are connected with aliens or the lost continent of Atlantis. Many non-experts have speculated that the spheres were used for astronomical purposes, while others think they may have pointed the way to significant places. However, the truth is unknown, as John W Hoopes, an anthropologist at the University of Kansas said in an interview in January 2016, the Chibchan people who once populated Costa Rica and other parts of Central America disappeared in the wake of the Spanish conquest, and the purpose of the spheres vanished with them.

It seems strange that, the stone spheres were often found in geometric patterns, such as triangles, rectangles or straight lines and in clusters of up to twenty. It is estimated that the majority of them are dated between 800 and 1200 BC and many of them were found near the remains of dwellings and in close proximity to the gravesites. However, how the ancient people of Costa Rica made the cylindrical stone spheres, remains largely a mystery.

Nevertheless, the existence of gold artifacts from about 800 AD indicates that the people living during that period were experienced at working with very high temperatures. It led some researchers to believe that the stones were moulded into their cylindrical shapes by extreme heating followed by cooling, to remove any outer layers of rock. Later, the shaped rocks were probably finished by polishing with sand or leather.

Today, only a few are known to be in their original locations, as many of them became popular as lawn ornaments. They adorn the town parks of Palmar Sur and Sierpe and several are housed in the National Museum in San José. Only in 2014, the great spheres are enlisted in the World Heritage Sites of UNESCO.