The hidden offices underneath Memorial Bridge have been locked up since 1976.

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

Go take a picture with the inventor of the daguerreotype photographic process.

A clone of a cloned tree that was so important it allegedly had its own guards.

A small triangle of DC grass is the final resting place of one of Sonny and Cher's songs.

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

The unique traffic pattern named for an influential urban planner is also known as the Pedestrian Scramble.

A brass plaque dedicated to a convicted cannibal hangs in the National Press Club, and that's not even the craziest part of the story.

This sandwich shop has a century-old elevator behind a sheet of plexiglass.

These recently uncovered walls are all that's left of Washington, D.C's first defense contractor.

The most accurate timepiece in the world.

A celebrity from the late Cretaceous period.

The "lovely red Vega" of the legendary record-settling pilot.

Cold War intelligence agents monitored communist embassies from an attic in a former pigeon coop.

Seemingly unremarkable items like empty sushi trays, chef hats, and freshness stickers are being preserved so future generations can look back on this beloved cultural import.

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

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

Rumor has it the uncarved lump behind the three famous suffragists is reserved for the first woman president.

A computer bug so primitive it was an actual insect.

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

A super-sized promotional trick that is now a D.C. landmark.

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

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

An obscure public service from the U.S. government that redeems burnt, moldy, and soiled old greenbacks.