Only diehard explorers and insatiable curiosity-seekers make the journey to see the Nazca Lines in Peru - one of the most baffling enigmas of archaeology. The mosaic lies at the end of a 500km, bone-battering bus ride from the capital, Lima, in an area known as the Pampa Colorada (Red Plain), which isn't the most hospitable place on Earth. Rain falls for half an hour every two years, making the plain drier than the Sahara and helping to preserve the Nazca Lines, which date back about 2,000 years. In and around the lines are symbols etched on a giant scale that can be viewed in full only from the sky. The draughtsmen, probably Nazca Indians, created the landmark by removing the iron-oxide coated pebbles that carpet the desert, exposing the creamy sand below. Nobody knows the meaning of the etchings. They could be anything from a running track to a calendar, which was the preferred theory of German mathematician Maria Reiche, who believed the lines told ancient desert dwellers when to plant and irrigate crops. In the 50 years until her death in 1998 at the age of 95, the researcher, nicknamed the Guardian Angel, oversaw the protected mosaic, which she described as 'a fragile manuscript'. To make it easier to see, she swept the lines. 'I went through so many brooms,' she once said. 'Rumours circulated that I might be a witch.' Erich von Daniken focused on Reiche's obsession in his blockbuster, The Arrival of the Gods: Revealing the Alien Landing Sites of Nazca. Von Daniken said the shapes indicated it was an airport for aliens. His claim may seem ridiculous, but the lines, which enclose a 500km square area, can be seen in their entirety only from the air. Today, visitors take a plane to view the etchings, which include a flower, a bulbous spider and a whale. Then there's the figure of a man whose head appears to be shrouded by an aura or encased in a space helmet, depending on how you look at him. Contrasting with the organic figures are geometric shapes, all offset by straight lines. Perhaps the attraction grew from the imagination and was an explosion of early art best viewed in the same light as cave paintings. Whatever the truth, the mosaic must be treated kindly. Since the death of the Guardian Angel it has come under attack from erosion and man - in the shape of rubbish dumpers and speculators who carve out illegal goldmines that scar the landscape. But unless aliens step down from the clouds, the mystery of the sands looks set to stay intact. No Nazca survives, nor does any known written record of their culture other than the lines. The statement they make is no doubt as extraordinary as those of Stonehenge or the pyramids, yet remains comparatively obscure, despite their bewitching presence ( www.peru.info ).