Visit the monolithic tomb of America's most famous general.

In upstate New York, gorgeous waterfalls and a watermill are slowly being reclaimed by nature.

The only home that Alexander Hamilton ever owned has a history almost as troubled as his own.

New York City's smallest piece of private property.

The "Seinfeld" diner.

An 18th-century townhouse that once hosted guests of the president.

One of the last mosaic tile facades found in the city.

While most wind tunnels test scale models, the "Cave of Winds" was large enough for actual airplanes.

Largest Roman Catholic church in North America.

A monument in Washington D.C. marks the spot from which all other roads were supposed to stem.

The story behind this beloved toy—named for Theodore Roosevelt and owned by his grandson—is more complicated than you might guess.

The legacy of a wealthy executive and his wife, this little-known art museum features works by Picasso, Monet, Renoir, Cezanne, and more.

The final residence of an educator, civil rights leader, and presidential advisor was also the first headquarters of the National Council of Negro Women.

Once a sewer culvert, this road tunnel now offers cyclists and pedestrians a subterranean stroll under the C&O Canal.

This taxidermy horse was a Civil War hero.

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

This robust fence in front of a historic Georgetown home is likely made from hundreds of recycled Revolutionary War firearms.

The remains of Martha, the last known passenger pigeon, serve as a tool to educate about conservation.

A celebrity from the late Cretaceous period.

The most decorated dog of World War I is preserved in the Smithsonian.

A derelict bit of transportation infrastructure hidden in the woods.

The site of the climactic scene from the classic horror film is now a historic landmark.

Surrounded by a verdant garden and a backdrop of ivy, a monument to beloved poet Khalil Gibran stands outside of the Lebanese embassy.

The oldest house in Washington, D.C. wasn't originally constructed in the nation's capital.