The mysterious giant spheres of unknown age, originally found in the jungles of Costa Rica and more recently in Mexico, Aruba, and Haiti, are so exactly round that it has been suggested that they are natural formations, although some of them show traces of tool marks. According to one theory they are representations of planets and moons of the solar system or systems and, if they had been left where they were originally place, would form a gigantic prehistoric planetarium.
(Photo courtesy of Carlos M. Peralta)

From Mysteries of Forgotten Worlds by Charles Berlitz