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

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

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

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

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

There's an old indoor swimming pool hidden directly underneath the White House Press Briefing Room.

The monument's pointy aluminum tip has been melted down by repeated lightning strikes.

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

The first presidential bomb shelter was located in an old vault under the Treasury, connected to the White House via tunnel.

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

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

A little marble compass above George Washington's (empty) tomb in the Capitol marks where D.C.'s four quadrants intersect.

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

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

The most accurate timepiece in the world.

Perhaps the most scandalous statue of America's first president.

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

The house where John Wilkes Booth conspired with his co-conspirators.

Largest Roman Catholic church in North America.

An atomic bomb-proof strongbox protects the U.S. Constitution from terrorists and thieves.

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

The oldest continuously operating fish market in the United States.

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

A hidden gem on the lawn of the U.S. Capitol Building designed by landscape architect Frederick Law Olmsted.