There's a crumbling old mansion inside the Smithsonian National Zoo.

The famous abolitionist’s preserved estate is one of Washington's finest monuments to its great Black citizens.

Government testing at the asylum briefly explored using marijuana as a "truth serum" on Nazi prisoners of war.

The oldest continuously operating fish market in the United States.

An Industrial Revolution-era public work that purified water using nothing but sand.

A nostalgic bibliographic gem.

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

The winding route passes through an enclosed alleyway, two tunnels, and leads to the White House basement.

Fittingly, America's museum of architecture is itself a magnificently designed old building.

A cavernous three-story, 43,800-square-foot basement that was forgotten about for 60 years.

There's a 12-foot-tall replica of the Washington Monument hidden under a manhole nearby.

One of the dwarven trees dates back to 1625 and survived the Hiroshima bombing.

Home to items never before seen by the public.

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

The United States Capitol's former columns still stand.

A line of blue paint marks the route of the inaugural parade.

Where the U.S. government kept its actual treasure, before Fort Knox.

Legend has it that President Grant’s frequent drinking in the lobby gave rise to the term “lobbyist.”

Must form and function forever remain at odds? Not if the Florida Department of Transportation has its way.

A statue honoring 44 continuous years of greeting passing ships.

This kitschy tavern is also home to rare early editions of "Treasure Island."

The 72-foot giant escaped confinement in a large patch of mulch only to be reburied in the sandy shores of the Potomac River.

Cairns built to bring travelers good luck stretch across the land like miniature stone mountains.

The picturesque birthplace of Icelandic democracy is drenched in the blood of its brutal past.