So...Nathan got a little Indiana Jones on you and was carried away by his own adventure story of Macchu Picchu, so he may have been just a wee bit off in his Macchu Picchu facts. Being the stickler for accuracy (and, incidentally, the beautiful wife of the heroic adventurer) I feel I must set you straight. Machu Picchu was not a last stronghold of the Incas, though that sounds pretty cool. Actually, it was abandoned less than one hundred years after being built in the mid-15th century, perhaps due to the devestation of smallpox. It's precisely because it was abandoned, however, that so much of it remains today. Because the Incas left before the Spanish discovered it, the city wasn't plundered or destroyed.
Though much remained when Hiram Bingham was led to Machu Picchu by a local Quechua boy in 1911 (while searching for another site that was the actual last stronghold of the Incas) it wasn't as neat and tidy as it is today. It was consumed by jungle vegetation, and we recently learned that it was burned in order to clear this vegetation. This only destroyed a little itty bit of the original stonework, so don't worry. Most of what we see today has been rebuilt and restored. Regardless, it is spectacular and an amazing architectural feat.
Nathan also neglected to tell you about the savage beasts and hungry cannibals we fended off with machetes and whips while climbing vines to reach the lost city of Machu Picchu. But that's just details.