The tallest stationary dunes on Earth also happen to sing.

The latest in a series of long glass bridges suspended at terrifying heights.

One of the world's largest ice festivals dazzles visitors for over a month with radiant sculptures and carvings.

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

For those with no fear of heights: a skywalk 4,700 feet up on a Chinese mountain.

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

270 million year-old forest of stone.

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.

This hilltop warren of monastic dwellings is the result of centuries worth of Mongol attacks.

Thousands of exquisitely carved stone water storage wells, hundreds of stone steps fill this exquisite medieval stepwell.

World's largest cave was only discovered in 1991, and now offers tours to the public.

Twice a day a speeding train passes only inches from the homes of this residential neighborhood.

This underground church is topped with a 500-foot cross that is seen by many as a beacon of fascist hubris.

Step inside the first house designed by Catalan architect Antoni Gaudí, considered to be one of the first Art Nouveau buildings.

A completely underwater art museum sends a stark message about humans' impact on the environment.

Spanning the El Chorro gorge, this pathway used to be one of the most dangerous crossings in the world.

Hundreds of stone stairs and a winding medieval bridge connect this haunting Spanish island to the mainland.

Three bridges and one giant canyon make up this fantastic Spanish settlement.

Bridge that died in war and was resurected.

A remarkable geological formation resembling a forest made of stone.

A set of ancient drawings in the desert of Peru that are so massive, many of them can only be fully seen from the sky.

Keshwa chaca, among the last handwoven Incan bridges, crosses Apurimac Canyon in Peru.

The largest stone moai on Rapa Nui.