The largest "man-made" earth structure is in Cahokia Illinois. What is buried underneath is insane.

 

What lies beneath the man made hillsides in Cahokia Illinois will blow your mind. According to Smith Journal these massive structures are filled with bodies.

Hundreds of bodies fill the grounds that are said to be “fertility and renewal” offerings.

Worth a road trip if you have the time, but something this is this real and this scary...I think I'm good.