The Inca Empire has held its mystery for five centuries in large part because it fell so quickly to Pizarro. Many of its secrets vanished with the empire itself, and remain matters of speculation. Machu Picchu actually survived the conquest because its existence itself was a secret. It became the quintessential lost city, and is as mysterious today as it ever was.
The Site and Getting There
The city (or palace, or ceremonial center) is built on a saddle-shaped mountain ridge perched on top of steep cliffs that drop down to the Urubamba river. It can be reached by foot on the Inca trail, or by a harrowing train ride from Cuzco. Companies like Alexander and Roberts offer private tours for travelers and are a good resource for a Machu Picchu trip: this is the city that inspired Indiana Jones, but you don't want to go through an action movie getting there.
The most lasting mystery of the Inca is their construction technique, and Machu Picchu is one of the best examples of it—certainly the most striking, though some sites use larger stones. The walls, steps, and objects like the mysterious Inti Watana are either carved directly in the living rock, or else dry-fit using sometimes enormous andesite boulders, perfectly carved like puzzle-pieces and fitted together.
Despite a range of suggestions from archaeologists and esotericists (and somewhat more practical suggestions from stonemasons), no one is entirely sure how they did this, let alone why.
Walls That Survive Earthquakes
Tourists in Cuzco will be familiar with this construction, because much of downtown Cuzco is built in the ruins of Inca stone buildings. In fact, the Inca walls are famous for surviving earthquakes, when the rest of the city has gotten wrecked. As impressive as the Cuzco is, though, its walls are fragmentary and covered in a modern city. Machu Picchu is something else entirely.
Since it was effectively untouched until 1910, Machu Picchu's stonework is largely intact. The conservation policy of the site has been to repair structures that have been damaged, so travelers see something very much like what the Emperor Pachacuti saw. Finally, and it is hard to stress this enough, the whole site is sitting on a two-thousand-foot volcanic pedestal: few places in nature are this picturesque, or this daunting to build a city on top of.
We may never know precisely why the Inca decided to come here. But they did. And now we come, too.