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

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

The most accurate timepiece in the world.

People escaping slavery may have hidden inside a corpse vault.

Once the supplier for noteworthy projects like the National Cathedral, this old brickworks now lies abandoned.

D.C.'s first central library was born out of a chance encounter with the philanthropist whose name it bears.

A historic ruin just 20 feet away from a busy highway onramp.

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

The privately owned cemetery that holds room for Washington's finest when they step down from life.

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

A computer bug so primitive it was an actual insect.

Light bulbs, scrap wood, and tinfoil comprise this homemade throne of the gods.

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

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

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

A Spiritualist house of worship where believers communicate with the dead in the spirit world.

Franciscan monks created a facsimile of the Holy Land for North Americans who couldn’t afford the trip overseas.

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

This lonely waterfront memorial to the men of the Titanic was erected by the "Women of America."

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

A nostalgic bibliographic gem.

This imposing Masonic temple a mile from the White House was the first public library in Washington, D.C.

Fittingly, America's museum of architecture is itself a magnificently designed old building.

A painfully obvious spy house sits right across the street from the Russian Embassy.