Have you heard about the Nasca lines? These lines are also called as "Riddles in the sand" were discovered in 1927 and are the giant ground drawings etched across 30 miles of gravel covered desert near Peru's southern coast. No one knows who has made these giant drawings on the ground. It is definitely impossible for humans to make such drawings.
Nazca lines are the lines etched in the surface of the desert pampa sand. Nearly 15000 figures made of straight lines, geometric shapes and pictures of animals and birds. Their pattern is only visible clearly from the air.
These Nazca lines are drawings of several kilometers in length and 0.4 to 1.1 kilometers in width drawn in different shapes like animals, geometric shapes and trapezoidal forms. You can see the figures of spider, monkey, astronaut, the dog, small lizard, the humming bird etc.
The Nazca lines are declared as "Archaeological World heritage Site" by UNESCO in 1994. These lines are located in Peru coastal plain some 400 Kms. from south of Lima. These lines were drawn on the surface of the ground between 500 BC and 500 AD. The lines can be clearly visible from an air plane in flight.
The Nazca lines are really a great mystery and no one knows how these giant pictures were draw. Some people believe that these lines are the signs left by some aliens or the landing strips for UFOs.
Here is a video about the mysterious Nazca lines.