The cathedral in the Spanish city of Salamanca was constructed in 1102, and is therefore one of the oldest such constructions in the world. It features magnificent stone carvings on all its walls, but one of them is a bit more special than the others, so to speak. It bears the depiction of what appears to be a fully dressed astronaut in a space suit, complete with details such as the sole of his shoes. Nobody knows how he got there, or what a 20th century astronaut is doing on the walls of a 12th century religious building.
Needless to say, the find has left all in a deep state of shock. There are, of course, numerous such mysteries in the world, ancient finds that have somehow caught us off guard, such as the old batteries found in Egypt, dated as being older than Christianity. But finding an astronaut carved between religious ornaments is no easy task to explain to conspiracy theorists, who, needless to point out, think governments have something to do with covering up the existence of aliens.
Some have argued in various writings that a good part of the technology and knowledge people have gained over time comes from extraterrestrial beings. And this would make a certain amount of sense, considering the advanced knowledge Egyptians displayed while building the pyramids.
The Inca benefited from revolutionary information, as well, when they built Machu Picchu, and the Mayan solar calendar is a true wonder of the world. Stonehenge in England is a nearly perfect solar observatory, and this makes people wonder how savages managed to raise such wonderful structures.