I believe these have all been explained scientifically how humans built them (except for the Mars thing). But I still believe- aliens.
7 Ancient Sites Some People Think Were Built by Aliens
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 civilizations managed to make some of the largest and most enigmatic constructions on Earth.
Sacsayhuamán (Peru)
Nasca Lines (Peru)
Egyptian Pyramids
Stonehenge
Teotihuacán (Mexico)
Easter Island
The Face on Mars
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Descriptions and cool pics at the link.