Gazing at the Andean peaks soaring above the Lost City of the Incas and the lush valley below, it's easy see why it was voted one of the New Seven Wonders of the World in 2007. The 15th century A.D. Peruvian site was abandoned shortly after Spanish conquistadors invaded the neighboring areas, falling to ruin until 1911, when an American scholar stumbled across the remains.

History's once glorious metropolises have become ever more sought-after destinations as Americans get back into travel mode. Machu Picchu welcomes as many as 1 million tourists annually, and that number is said to be growing as much as 6% per year.

The Americas offer travelers dozens of lost cities to explore. Mexico has the Mayan city of Chichen Itza, with Mesoamerica's largest ball court and the hulking pyramidal remains of Teotihuacan, with its well-preserved, color-splashed murals. There's Tical in Guatemala and Copan in Honduras. Even the the Western U.S. boasts the tumbleweed-strewn ghost towns of two centuries ago.