Sacsayhuaman, Peru

Emperor Pachacuti (or Pachacútec) began building the hillside citadel in the 1440s, but the massive complex wasn't completed until nearly 100 years later. Today only a fraction of the original structure still stands, the rest having been torn down by the Spaniards to build houses in Cusco. What does remain, however, is remarkable.

The most impressive feature might be the massive 66-foot-tall (20-m) outer walls, which are still intact and zigzagging together like razor-sharp teeth, having withstood battles, earthquakes, and time. Even though the largest of the stones weigh over 300 tons, they are fitted perfectly, in the Inca style reserved for important structures. It is believed that in ancient times, this area was probably used for ceremonial gatherings. Today, visitors may be lucky enough to catch one of the many sun ceremonies still held throughout the year.

In 1536, the fort was the site of one of the bitterest battles of the Spanish conquest, sparked by Manco Inca’s rebellion. The Incan resistance leader’s army managed to seize Sacsayhuamán from the Spanish, one of the only victories of the native people against the conquistadors. The triumph was short-lived, however, and 50 Spanish cavalry led by Juan Pizarro, Francisco’s brother, succeeded in recapturing Sacsayhuamán and essentially ending the rebellion.

While Manco Inca survived and escaped to the fortress of Ollantaytambo, most of his forces leapt to their death from the high towers to avoid being killed by the Spanish. The next morning, condors feasted on the pile of corpses, an image captured forever on Cusco's coat-of-arms.

In Quechua the name Sacsayhuamán means “satisfied falcon,” though it’s often referred to mnemonically – “sexy woman” – by travelers.