The location is Teotihuacan, or beneath it, to be more precise. It is a massive ancient city, which lies on the outskirts of Mexico City. And while, in many ways, her modern sister has dwarfed and surpassed her, Teotihuacan still holds a few secrets for those willing to send in a pack of excavating robots in their stead.
A team of archaeologists, lead by Sergio Gomez Chavez has been planning the excavation for quite a few years now. During that time, it was decided that robots would make the best excavators for the chambers below the Temple of the Feathered Serpent. This is due to the robots' smaller profile and the dense, haphazard nature of the earth packed below the temple — earth that was deposited there deliberately by the residents of Teotihuacan before they vanished (all 100,000 of them) in 700 A.D.
The reasons for their departure are entirely unknown, but one of the reasons that they filled in the spaces below their sacred temple is. A large number of dull yellow spheres have been discovered in one of the subterranean chambers. The spheres are thought to once have been smooth, glistening balls of golden wonder. Today, they are but orbs rough around the edges and more of a yellow color than gold.
That's because they're actually an oxidized form of Pyrite, or Fool's Gold. Despite that fact they aren't made from the real stuff, scientists are still baffled by what purpose the long-buried orbs held for their people. Research will carry on until they do have an idea, though. There are also three more chambers to be excavated beneath the Temple of the Feathered Serpent, one of which, it is rumored, was partially demolished 1,800 years ago so that "something very important" could be hidden there by the residents of Teotihuacan.
Who knows what mysteries are yet to be made in Mexico City's ancient neighbor. Time, and robots, will tell.