Ghost of a flea

The stone city, made up of five citadels at 9,186 feet above sea level, stretches over around 39 square miles and contains walls covered in carvings and figure paintings, exploration leader Sean Savoy told Reuters.

"It is a tremendous city ... containing areas with stone etchings and 10-meter (33-foot) high walls," said Savoy, who had to hack through trees and thick foliage to finally reach the site on Aug. 15.

Covered in matted tree branches and interspersed with lakes and waterfalls, the settlement sites also contain well-preserved graveyards with mummies with teeth "in almost perfect condition," Savoy said.