S1, E6: The fate of entombed treasures, including the contents of a mysterious "doomsday vault," the "Mona Lisa" and the Declaration of Independence; Philadelphia's Liberty Bell cracks for good; San Francisco cable cars and bridges snap.

S1, E6: The fate of entombed treasures, including the contents of a mysterious "doomsday vault," the "Mona Lisa" and the Declaration of Independence; Philadelphia's Liberty Bell cracks for good; San Francisco cable cars and bridges snap.