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

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

The bank that helped fund the Mexican-American War and the purchase of Alaska met its downfall after helping Augusto Pinochet launder money.

Four bald cypress trees in Lafayette Square, across from the White House, mark the southern edge of a 100,000 year old cypress swamp.

D.C. once had its own tiny rival to the New York Stock Exchange.

This nine-story building is the oldest standing skyscraper in D.C.

A three-story tower of books about Abraham Lincoln is one of the more unusual monuments to the president.

The oldest continuously operating fish market in the United States.

This lovely picnic spot featuring thunderous jet landings is an aircraft spotter’s dream.

This isn't your average roadway—it's actually a National Park and a transportation pioneer.

This brick-lined pedestrian walkway was once a railway tunnel used during the Civil War.

Once forgotten and built over, this historic Black cemetery now houses a poignant memorial.

The graveyard holding the remains of George Washington's slaves was forgotten for nearly 200 years.

The tomb was guarded by soldiers from both sides of the war, and some left their initials carved in the brick.

The only place for a truly presidential dram.

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

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

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.

Members of Congress have traveled between the buildings on Capitol Hill for a century hidden from tourists, press, and storm clouds.

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

"Congress may voluntarily remain in session throughout the summer, in order that our Congressmen may be protected from the intolerable discomforts and dangers of the ordinary outdoor weather!”

The only National Monument ever to go missing for nearly 50 years then resurface in a dump.

The beloved statue at the National Academy of Sciences is oh so inviting to sit on.

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