Two New York rooftops are home to the largest rooftop soil farms in the world.

A hidden passageway now marks the site of an assassination attempt on Ronald Reagan that some say broke a 140-year-old curse.

A 1,100-ton train fell through the floor in 1953. Workers got it patched up in just 72 hours.

A promising candidate for the lost rock laid by George Washington was unearthed, but the hunt is still on.

An ear-piercing buzzer calls lawmakers to a vote with a series of long and short rings to form coded messages.

Part of a WWII submarine is lurking outside the Washington Navy Yard parking lot.

A muscular Art Deco monument represents the struggle between regulators and unbridled markets.

The elevator that makes it possible to fly American flags in bulk over the U.S. Capitol

One of the most influential presidents in U.S. history wanted only this plain, elegant monument as his lasting memorial.

A building shaped like the Army Corps of Engineers logo, because why not?

The fountains of the U.S. Navy Memorial are annually salted with water from the Seven Seas as part of a nautical ritual.

Before founding the American Red Cross, Clara Barton had a tremendous humanitarian impact by locating thousands of missing soldiers.

When it comes to handsignals (and colonialism) rock always beats scissors.

They sort through millions of dollars worth of diplomatic gifts on behalf of the government.

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

A bas relief commemorates the "Nuns of the Battlefield" who cared for soldiers on both sides of the conflict.

The discovery site of the "Capitalsaurus," the official dinosaur of Washington, D.C.

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

This unacceptably tall building was the real reason for Washington, D.C.'s skyscraper ban.

This forgotten boat elevator was an engineering marvel in its heyday.

The oldest building in the District of Columbia was preserved because of a mistaken connection to George Washington.

Architecture lovers won’t stop touching the National Gallery's 19.5 degree marble prow.

Before Nixon, "watergate" meant canals.

A tiny monument to the unsuccessful attempt by Thomas Jefferson to place the prime meridian in Washington.