Behind an abandoned storefront is an example of pioneering 1930s gas station architecture.

One of the largest artillery pieces in the world sits in a Washington D.C. parking lot.

A heroic pigeon that, through a barrage of gunfire, delivered a message that saved over 100 lives in World War I.

A three-story tower of books about Abraham Lincoln is one of the more unusual monuments to the president.

There’s a hidden military meme engraved on the World War II Memorial.

This quirky UFO-shaped curiosity is often mistaken for the airport’s control tower.

One of the few remaining examples of 19th-century London’s attempt to clean up its reputation.

A monument to the thousands of Canadian soldiers who died capturing the French ridge during World War I.

The elegant manor house where Kaiser Wilhelm II lived in exile after World War I.

The first mosque in the world to receive electricity.

This bug-eyed water wheel uses the power of the Sun to clean up Baltimore Harbor.

It's not hard to see why the historic Peabody Conservatory of Music's library has been described as a "cathedral of books."

On the Fourth of July this area will transform into a Pompeii-like storm of falling embers and ash.

This taxidermy horse was a Civil War hero.

This seemingly out-of-place gas station by the Watergate hotel was once described as the most expensive gas station in the world.

A historic arena where the Beatles played their first concert in the U.S.

This sandwich shop has a century-old elevator behind a sheet of plexiglass.

During the Industrial Revolution this “Temple of Invention” was full of intricate miniature machines and gadgets.

With over 100 jam-packed rooms to explore plus elaborate tea services and events, the Mansion on O Street is a hidden treasure.

You can walk through the first Boeing Air Force One, which famously carried JFK's casket from Dallas back to D.C.

A pyramid commemorates the birthplace of James Buchanan, the 15th president of the United States

Color-coded signs direct drivers on a network of routes designed to avoid Pittsburgh traffic.

A dramatic, 360-degree recreation of Pickett's Charge in the Civil War.

This shrine to McDonalds' most iconic sandwich holds a 14-foot tall burger.