Take a Google earth tour across most of eastern Mexico. That jungle could hide a couple of Manhattan islands worth of buildings. Most of earth is like that, unknown. Or, at least unrecognized.
Did some dingbat monk(ish) walk over some weird spot and come back with incredible stories? Sure. But, why believe some guy who WANTS to avoid his neighbors?
#3 I was looking for the Kingdom of the Crystal Skull and came across a few hidden Mayan cities.....