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

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

People escaping slavery may have hidden inside a corpse vault.

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

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

Art deco landmark on the outskirts of Washington, D.C.

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

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

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

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

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

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

A traveling postal dog covered 48 states and more than 140,000 miles, and he lives on as taxidermy, patched up with a rabbit's foot and a pig's ear.

The beloved statue at the National Academy of Sciences is oh so inviting to sit on.

A historic estate packed with George Washington's heirlooms, and its own nuclear bunker.

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

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

A haunting tribute to pioneering photographer Clover Adams.

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

The walls of the iconic dome are hollow and have a secret stairway.

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

A lovely aquatic park built by a one-armed Civil War veteran who made a fortune from lotuses.

A derelict bit of transportation infrastructure hidden in the woods.

A cavernous three-story, 43,800-square-foot basement that was forgotten about for 60 years.