Staying in a hotel in Cuzco, my wife and I got to examine the famed Inca stonework up close; one of the walls in our room was composed of the original Inca foundation--interlocking stones fit so precisely, without mortar, built with no metal tools...

Andean history makes up the literal foundations of this Peruvian city: the colonial Spanish architecture sits atop the Inca foundations that line the streets. The pre-columbian architects knew how to build. In the numerous earthquakes that have shaken Cuzco over the centuries since the Spanish conquest, the European architecture topples every time; the Inca walls have never fallen.

(Above: on the left--the famous 12-angled stone on a side street in Cuzco; center--the 'jaguar's paw' in Sacsayhuaman fortress in the hills above the city; right--a typical Inca-stone-lined street in the historic center.)