A historic train ride from California to Mexico.

This tall stone wall with no door and ill-matched windows was built centuries ago, and used as a shelter for domesticated pigeons.

Often referred to as the largest spring in America.

According to legend, this ancient column contains healing properties.

This environmental engineering marvel keeps salt water from the Elizabeth River.

One of the Treasury Building's original columns now sits as a garden monument in the middle of a busy military base.

Using a massive antenna made up of five miles of wire, two scientists tuned into organic radio waves from the planet Jupiter.

This bizarre hotel on historic Route 66 has been plagued by rumors of paranormal activity.

A fortress on this island housed the mysterious prisoner known as the "Man in the Iron Mask" for more than a decade.

Hidden in the New Mexico desert southeast of Roswell, nine small deep lakes formed inside sinkholes.

A beachside cave filled with Bronze Age metalwork, pottery, and human remains.

This building, previously used as a courthouse, has an unusual geological feature in its basement.

An ice field known for harboring an infamous Martian meteorite turned out to contain the oldest air on Earth.

One of the biggest mysteries of Central Queensland: How did this truck spontaneously combust with the force of a massive bomb?

This ancient stone bridge dates back to the early Middle Ages.

The world's only full-size replica of the research hut used by Douglas Mawson for his 1911-14 Australasian Antarctic Expedition.

This stone once marked the boundaries of Liverpool's medieval markets.

These oldest of these "embroidered stones" were carved 4,000 years ago in a high mountain valley.

This crumbling coast and its teetering tower are literally filled with history, but they are also at great risk of becoming history themselves.

This little-used trail winds through the highest mountain range in central Nevada with sections around 10,000 feet.

After serving in World War II and picking up Apollo astronauts, this aircraft carrier has been turned into a museum overlooking the San Francisco Bay.

This church is named for one of the most dramatic tales in the early Christian church.

Located in the middle of public park, this cave built in the early19th century houses an ancient stone sarcophagus.

The largest Roman amphitheater in the Balkans once held over 20,000 people, but managed to lay hidden for hundreds of years.