Housing the National Women's Party since 1929, this historic house is now a monument to the fight for gender equality.

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

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.

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

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

A haunting tribute to pioneering photographer Clover Adams.

A derelict bit of transportation infrastructure hidden in the woods.

The country's oldest continually-operated mini golf course lies hidden in plain sight, eclipsed by one of D.C.'s most popular tourist attractions.

During the Industrial Revolution this “Temple of Invention” was full of intricate miniature machines and gadgets.

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

A wondrous old library overlooking the nation's capital.