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.

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

A derelict bit of infrastructure from the canal that once ran through D.C. is landlocked in the heart of the city.

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

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

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

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

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

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

An overlooked memorial honoring the local Washington residents who died in World War I.

The institution is sitting on a goldmine of 21,000 paints, varnishes, pigments, and primers preserved for posterity.

The early data processor factory founded in Washington for the 1890 U.S. Census went on to become IBM.

A fantastic array of trays and cables once whisked books over to the Capitol at 600 feet per minute.

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

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

Those with a sharp eye can find the hidden image of a German Shepherd on the memorial's Mural Wall.

The U.S. Navy’s preposterously detailed mini battleship took 77,000 hours to complete.

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

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

For 60 years, the academy had no permanent location until members voted Washington D.C. as its forever home.

The 28,000-year-old specimen is remarkably intact.

A secret greenspace hides atop a Capitol parking garage.

Amid the sprawling Defense Intelligence Agency Headquarters is one of Washington's least accessible museums.

An amazing example of early-20th-century architecture, this church features marble transported from Utah.