The multinational team, including Britons, has located the site in a remote region in central Ecuador which it believes could represent one of the great archaeological discoveries.
They have already unearthed a 260ft tall by 260ft wide structure, made up of hundreds of two-ton stone blocks, and believe there could be more, similar constructions over an area of about a square mile.
Investigations of the site, in the Andes mountain range, are at an early stage and theories as to what it contains vary.
Some of those involved believe it could be the mausoleum of Atahualpa, the last Incan emperor who was captured by the conquering Spaniards, or hold the Treasure of the Llanganates, a vast haul of gold and other riches amassed by his followers to pay for his release.
... Others believe the newly discovered site dates back far earlier, to unknown, pre-Inca cultures from before 500 BC, citing what appear to be rudimentary tools found there.
Local legend has it that the area was once populated by a civilisation of exceptionally tall people and the apparently outsized nature of some of the approximately 30 artefacts found have led some to describe the area as the Lost City of The Giants.
The site, in the Llanganates National Park, is being investigated by a team of British, French, America and Ecuadorean explorers.