An abandoned saucer-shaped monument in the Bulgarian mountains.

Hundreds of caves filled with thousands of centuries-old statues and murals.

Climb atop one of the world's longest and heaviest trains for an unbelievable journey across the Sahara Desert.

The singular ruins of a mysterious lost city.

The city of Palestrina was built around this magnificent terraced sanctuary dedicated to the pagan goddess Fortuna.

The tower in this 1,000-year-old mud-brick village seems to vibrate for no apparent reason.

One of the most well-preserved temples of ancient Egypt.

Known as the leaning temple, the sacred structure has somehow developed a severe nine-degree slant.

Where the Great Wall of China meets the sea.

A mesmerizing reservoir nestled at the heart of a pre-Islamic Yemeni village.

The ancient water tanks remain some of the ruined city’s most beautiful architecture.

Hidden in the shadow of a rocky fortress is one concubine’s long-forgotten legacy.

This magnificent stepwell is designed as an inverted temple and adorned with 1,500 sculptures.

After the parade, students throw their beads on the tree hoping for good luck on exams.

This rare example of a "tidefall" is a spectacular drop from the cliffs down onto the beach.

The ruins of an Estonian prison are drowning in the quarry lake where the convicts were once forced to work.

Life in this isolated, hilltop lighthouse was lonely, but it sure was lovely.

Elephant seals and sea lions have turned the abandoned buildings on this island into their endangered love shack.

A lonely beacon, precariously perched atop a remote sliver of rock.

This meticulously extracted nervous system allegedly came from a 19th-century custodian who donated her body to science.

There's an exclusive Beefeaters pub hidden in the Tower of London.

Reaching the "Church in the Sky" requires scaling the cliff face of a sandstone pinnacle with a 650-foot drop.

This sublime architectural marvel is a rare example of an expressionist church.

Far from the shore, this sandy victim of the Skeleton Coast looks like it was plopped in the middle of the desert.