The Nazca lines. In the town of Nazca I took a little plane up to see the famous lines. I was surprised at how many geometrical ones there were. I had only heard about those shaped like animals. This was 2001.
There are lots of lines spread over a vast area. This took a lot of work and their purpose is mysterious. Obviously they are best viewed from the air. They don’t even know why they exist. Theories abound from the typical stating they were used for religious purposes or to summon water to them being built for extra terrestrials. I saw one theory that it is a giant primitive loom for making of textiles to cover mummies? Aliens makes more sense to me than a loom.
They don’t know when they were made either. I have heard estimates of 600-200BCE up to 700CE.
Like most things the lines face modern threats. They have been damaged by truck drivers taking shortcuts, Greenpeace activists, squatters, mining equipment etc.