Across Valencia lie the remains of three ancient fortifications built centuries apart: a Roman enclosure, an Islamic expansion, and a medieval Christian wall.

This fort down the Potomac from Washington, D.C. was once the only defensive fort protecting the capital.

A majestic hotel that also stands as a historic relic.

This staircase in a lush tropical grotto was built by enslaved laborers and renamed to honor Queen Victoria's role in ending slavery in the British Empire.

Commercial airplanes land mere feet over the heads of sunbathing beachgoers on this tiny island.

Come for the springs; stay for the mud bath.

The larger of two volcanic peaks rising out of the crystalline waters of the Caribbean.

Rumored to be the famed pirate's lookout tower, this historic stone structure is now just watching for tourists.

This huge pile of volcanic boulders hides a stunning network of secret grottoes.

A Roman bridge closed to car traffic in the 1990s now open to foot traffic.

The city of Parma's cathedral is home to one of the greatest illusionistic frescoes of the Renaissance.

One of the world's oldest working clocks is curiously missing the Zodiac sign of Libra.

One of the largest squares in Europe contains an entire artificial island.

Go inside to really appreciate this 500-year-old technological masterpiece.

An iron dragon with a long neck covered in feathery scales perched above one of Venice's most popular squares.

In the past, Renaissance sex workers were encouraged to entice customers on this bridge.

Two stone columns flank the grand Venice square, but there were supposed to be three.

This palatial spiral staircase was so unusual the name "snail" was given to the noble family who built it.

The rounded structure has evolves from service station to citrus to souvenirs to Charley survivor.

Take a ride inside a former coal mine in Ashland, Pennsylvania.

A living history village recreates a vanished 19th century community.

This ancient Roman cistern has been the source of many legends throughout the centuries.

Decorative folk arts dot the countryside barns of Berks County. 

Descend into the world’s longest-running deep anthracite coal mine.