Helen Keller once broke ground on this historic center for the study of technologies to benefit the hearing impaired.

100 years later, they're still down there.

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

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

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

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

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

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

The towering figures were created from the cemetery's fallen old-growth trees.

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

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

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

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

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

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

A hoard of sky catalogs, astrophysical journals, even the works of Galileo and Copernicus.

Decades before the scandal, this staircase on the river was a literal "water gate."

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

The most accurate timepiece in the world.

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

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

This stunning blue and gold room changed cities twice before becoming part of the Smithsonian.

A computer bug so primitive it was an actual insect.

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