A luxurious 1880s hotel with its fair share of Tiffany stained glass, Edison electricity, and of course, ghosts.

Location of a reliquary containing bone fragments of 18 saints.

An original apothecary from 1792.

One of the most influential presidents in U.S. history wanted only this plain, elegant monument as his lasting memorial.

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

This sandwich shop has a century-old elevator behind a sheet of plexiglass.

The monument's pointy aluminum tip has been melted down by repeated lightning strikes.

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

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

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

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

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

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

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

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

Largest Roman Catholic church in North America.

Bar full of oddities, specimens, artifacts and homages to the great dime museums of the past.

A monument in Washington D.C. marks the spot from which all other roads were supposed to stem.

Long-abandoned trolley tunnels just a mile away from the White House are turning into an art space.

One of the dwarven trees dates back to 1625 and survived the Hiroshima bombing.

A tiny piece of the Moon is embedded in this stained glass masterpiece.

The sci-fi villain is a little-known inhabitant of the U.S. capital's largest cathedral.

Home to items never before seen by the public.

With over 100 jam-packed rooms to explore plus elaborate tea services and events, the Mansion on O Street is a hidden treasure.