Machu Picchu isn't a "lost city," as many tourist brochures would have you believe. It was simply a summer hangout for the Inca king. Undiscovered by Spanish conquistadors, it wasn't until 1911 that American explorer Hiram Bingham broadcast Machu Picchu's secrets to the world. The site is now Peru's most-visited tourist attraction.
Completed around 1450, Machu Picchu is an undisturbed masterwork of Inca craftmanship nestled high in the remote Andes. Supporting as many as 750 residents during the summer months, the seasonal retreat is a carefully-planned patchwork of homes and temples held up by a mammoth network of underground walls. Acres of terraced farms notched into the Andean mountainsides provided the settlement with food.
Most amazingly, the entire city is constructed from interlocking walls of smooth, polished stones. Without using mortar, the Inca fit the stones together like an immense jigsaw puzzle. Their work was so precise that, even after centuries of earthquakes, in many places it's still impossible to slip a piece of paper between the seams of two Machu Picchu stones.
The mystery of Machu Picchu is how the Inca were able to move such large stones to such a remote location. Although the rock was quarried locally, workers would still have needed to hoist 20-ton stones up steep mountain cliffs -- an especially grueling task when you consider that the Inca didn't use wheels. Ultimately, the coming of the Spanish conquistadors was so devastating to the Inca that within a generation after the arrival of Europeans, nobody was left alive to recall the secrets of their mountaintop city.