Senators used to relax in the nearly forgotten marble tubs now hidden in the U.S. Capitol Building's basement.

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

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

This poor little statue is the most vandalized memorial in Washington.

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

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

In the basement of the U.S. Capitol Building is a hidden storage room full of ornate floor tiles leftover from the 1850s.

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

An overlooked oasis of quiet on the grounds of Washington's monumental basilica.

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

This lovely pocket park is one of the most under appreciated in D.C.

The most accurate timepiece in the world.

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

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."

Home to a vast and influential collection of Shakespeareana.

A computer bug so primitive it was an actual insect.

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

This leafy estate is worth $18 million and is so grand it has two mailing addresses.

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

A Civil War fort in the middle of Washington, D.C. has been swallowed by a forest.

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

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

The Byzantine, pre-Columbian, and medieval art at this stately mansion are some of the most under-appreciated collections in D.C.