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

It was once the base for a series of domestic terror attacks.

This public park was the site of the largest civilian disaster of the Civil War.

A super-sized promotional trick that is now a D.C. landmark.

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

The sci-fi villain is a little-known inhabitant of the U.S. capital's largest cathedral.

A much-maligned monument to teetotalism.

Look closely and you’ll notice that the color changes a third of the way up the tower.

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

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

Rumor has it the uncarved lump behind the three famous suffragists is reserved for the first woman president.

The "lovely red Vega" of the legendary record-settling pilot.

A computer bug so primitive it was an actual insect.

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

Mysterious 500-year-old tapestries depict a unicorn hunt.

This once-grand marvel of engineering is now 41 miles of scenic hiking trail.

100 massive sculptures in the Hudson River Valley.

Creek water that starts here has a 50/50 chance of ending up in the Atlantic or the Pacific.

The only natural lake in the world that drains into both the Atlantic and Pacific Oceans.

The 5.5-mile ring of steel posts around the Capitol Building is one of the largest (and most uniform) of its kind in the world.

Manatees congregate around a power plant's discharge canal where the water is especially warm.

This rural community has attracted both scientists and techno-refugees due to its federally-mandated lack of technology.

A tradition unlike any other, this marks the site of the annual Groundhog's Day tradition.

The house that Frank Lloyd Wright "(shook) out of his sleeve at will" at the age of 86.