The UnXplained: Temporada 1, Episodio 11

Abandoned cities. Ancient cultures nearly erased by time. And colossal empires that simply vanished without a trace. How does a civilization become "lost"' What could cause once-thriving groups of people to just abandon their great cities, never to return' Can modern scientific knowledge help answer the unsolved questions surrounding these lost civilizations, or is there something more mysterious at work'.