Six ravens are kept captive (but well-fed) at the Tower of London to prevent the fall of the Crown.

The watery entrance for condemned prisoners heading to the Tower of London is still visible along the Thames.

The tallest bridge in California was constructed for a project that was eventually cancelled.

A scrap-metal sculpture recalls an infamous 19th-century camel.

This memorial pyramid marker honors one of the United States Government's first official camel riders.

The massive, incredibly rare instrument is over 11 feet tall with a range so deep it goes lower than humans can hear.

Home of Howard Hughes' Spruce Goose.

The wooden airship was the largest flying boat ever built.

Art Deco stylings conceal the true nature of this bridge.

Tucked away in the Tower of London is the weapon once used to execute high-profile prisoners.

Where a railroad loops under or over itself to rise or drop more than 70 feet in a short distance.

The Great Fire of London and the regulation of one-way streets both started in this alley.

The southernmost outpost of the Russian Empire in colonial America.

The commemorative stone column conceals a secret laboratory.

The largest wooden building in the world now houses a fascinating collection of aircraft.

This unassuming cheese empire in rural Oregon churns out more than 150,000 pounds of cheese each day.

The Denver airport is guarded by a 32-foot-tall sculpture of a demonic horse.

The only visible piece of San Francisco's most famous shipwreck.

This concrete tangle of square pipes has stood as a proud thorn in the city's side since the '70s.

Located within a historic park, the beacon is the oldest standing structure in Miami.

Bill Murray bowled three straight strikes here at Reno's "Taj Mahal of Tenpins."

Some of the tallest ancient American ruins continue to inspire awe and curiosity.

A geological mystery on Camelback Mountain.

This tiny cluster of abandoned buildings looks like the future of the ghost town - today!