These spots might not have been crafted by extraterrestrials, but that doesn’t mean they’re not out of this world. Planet Earth is home to some spectacular relics from bygone eras, constructions that seem to defy the technological capabilities of their time either because they’re too big, too heavy, or too complex. As such, some suggest the ancient builders of the Egyptian pyramids, the Nasca lines, and others were following an extraterrestrial instruction manual. Perhaps the hands that crafted these sites weren’t really of this world. To be sure, it’s fun to think about whether aliens have visited Earth. After all, humans are on the threshold of expanding our reach in space, and places like Mars are in our sight. But the truth is, there’s no evidence suggesting that aliens have ever been here. And invoking a supernatural explanation for some of the most monumental of human achievements means skipping over the fascinating ways in which prehistoric civilisations managed to make some of the largest and most enigmatic constructions on Earth.