The Largest City     

   Underground. 
  
   Bigger than Minnesota. 
  
   Excavation volume equal to 4,000 pyramids of Giza. 
  
   About 200 million structures. 
      This "city" was not built brick by brick, but grain by grain. By termites. 
Over some 3,800 years.

   The only visible structures are conical mounds, each about 8 feet tall and 30 feet wide. They are spaced about 60 feet from each other. 

   How do generations of termites do that? Like, how do honey bees make perfect combs, working from the perimeter toward the center? 

   If you wish to visit 88,000 square miles of termite city, this is in Brazil. 
But, don't come back with any of its inhabitants as souvenirs!!!

Study published in Current Biology