Thanks to 3D mapping, archaeologists have found the ancient Mayan city of Holtun, or Head of Stone. It's been long known that something was there but because of centuries of jungle covering the area, it was nearly impossible to know exactly what it was. The 3D topographical map effectively 'erased' the rain forest growth and revealed a pyramid, an astronomical observatory, a ritual ball court, numerous plazas, and hundreds of buildings.
According to Kathryn Reese-Taylor, a Preclassic Maya specialist, the Lost City of Holtun "was not a New York or Los Angeles, but it was definitely a Denver or Atlanta." Such a discovery is important so archaeologists can better understand how Mayans lived, worked and traded in these smaller, 'secondary' cities.
The Head of Stone site had actually popped up on archaeologist's radar back in the early 1990's thanks to looters who found the site first but the extent of what was hidden was never known—it's an entire freaking city after all! Read more about the find at National Geographic. [National Geographic, Red Orbit]