This ancient Greek place of assembly and marketplace is being revealed layer by layer below the modern Athens cityscape.

Monasteries on rock pillars, once accessible only by frayed ropes.

150 or so scrounged-up lamps, chandeliers, and lanterns light up this alley in central Athens.

Hidden in a secluded Greek cove is a pristine beach marred only by the rusting smuggler's hulk stranded on its shores.

The hallucinogenic center of the ancient world.

A spectacular cave and a beguiling lake.

A town church once nearly submerged by the damming of a river is now hauntingly visible as the water recedes.

The largest stone moai on Rapa Nui.

The intricate stonework of Machu Picchu serves as a testament to Incan engineers.

An emerald-green grotto just a short trip from Austin.

An Italian crevasse filled with abandoned buildings gives visitors a look at the world without humans.

This jaw-dropping 19th-century bridge uses its reflection to form what appears to be a perfect circle.

Most-visited and most-photographed slot canyon in the American Southwest.

The mysterious, fantastical woodland inspiration for "The Lord of the Rings."

Rippling sand dunes frozen in the Arizona rock.

This astonishingly geometric cave has inspired everyone from Jules Verne to Pink Floyd.

The world's longest outdoor escalator takes visitors to the top of China's largest dam and is also shaped like a dragon.

This vertical pinnacle in China was the inspiration for the floating mountains in the movie “Avatar.”

Not one, not two, but three natural bridges remain in this captivating spot post-sinkhole.

999 stairs lead visitors through a massive hole in a mountain known as the Gateway to Heaven.

A canvas of crops grow from vibrant red soil in this terraced farmland.

Intensely colorful calcite pools in Southern China.

A part of the world's largest marsh seems to be growing bright red Martian grass.

A fifth-century temple improbably built into the side of a cliff.