There is a legend believed till today that the Mayan Indians left 13 crystal skulls which were not human made and belongs to a different world or ancient advanced civilization. The first skull was found in 1920's. Only 8 of the 13 are found till today. Other skulls are still in quest. A real crystal skull was discovered by a British explorer, in an ancient Mayan temple deep in the jungles of Central America, back in the 1920's, whilst on a quest for the lost civilization of Atlantis. The nazca lines are not so close that you can see in the movie, there are no cliffs like the one depicted north of the lines. The lines are shallow designs made in the ground by removing the ubiquitous reddish pebbles and uncovering the whitish ground beneath. They do not appear like almost painted white as depicted in the movie.